Potential PSBT issues found by the PSBT fuzzer (#17136):

```
$ src/test/fuzz/psbt
…
==8112==ERROR: AddressSanitizer: heap-use-after-free on address 0x6070001083f0 at pc 0x55a5d650f41b bp 0x7ffe03cc3c90 sp 0x7ffe03cc3c88
READ of size 8 at 0x6070001083f0 thread T0
    #0 0x55a5d650f41a in CTxOut::operator=(CTxOut const&) src/./primitives/transaction.h:133:7
    #1 0x55a5d8362e8d in PartiallySignedTransaction::GetInputUTXO(CTxOut&, int) const src/psbt.cpp:72:14
    #2 0x55a5d6dae419 in AnalyzePSBT(PartiallySignedTransaction) src/node/psbt.cpp:32:19
    #3 0x55a5d64b27d7 in test_one_input(std::vector<unsigned char, std::allocator<unsigned char> > const&) src/test/fuzz/psbt.cpp:28:35
…

$ src/test/fuzz/psbt
…
AddressSanitizer:DEADLYSIGNAL
=================================================================
==22238==ERROR: AddressSanitizer: SEGV on unknown address 0x6098001079e0 (pc 0x55880d55c50f bp 0x7fff8d03d8f0 sp 0x7fff8d03d860 T0)
==22238==The signal is caused by a READ memory access.
    #0 0x55880d55c50e in CTxOut::operator=(CTxOut const&) src/./primitives/transaction.h:133:7
    #1 0x55880f3b6a83 in SignPSBTInput(SigningProvider const&, PartiallySignedTransaction&, int, int, SignatureData*, bool) src/psbt.cpp:262:14
    #2 0x55880f3b81ff in FinalizePSBT(PartiallySignedTransaction&) src/psbt.cpp:311:21
    #3 0x55880d500ee9 in test_one_input(std::vector<unsigned char, std::allocator<unsigned char> > const&) src/test/fuzz/psbt.cpp:62:11
…

$ src/test/fuzz/psbt
…
node/psbt.cpp:82:26: runtime error: signed integer overflow: 7857790368227518552 + 6582955728264977243 cannot be represented in type 'long'
    #0 0x55a8b66b13ee in AnalyzePSBT(PartiallySignedTransaction)::$_0::operator()(long, CTxOut const&) const src/node/psbt.cpp:82:26
    #1 0x55a8b66b1043 in long std::accumulate<__gnu_cxx::__normal_iterator<CTxOut*, std::vector<CTxOut, std::allocator<CTxOut> > >, long, AnalyzePSBT(PartiallySignedTransaction)::$_0>(__gnu_cxx::__normal_iterator<CTxOut*, std::vector<CTxOut, std::allocator<CTxOut> > >, __gnu_cxx::__normal_iterator<CTxOut*, std::vector<CTxOut, std::allocator<CTxOut> > >, long, AnalyzePSBT(PartiallySignedTransaction)::$_0) /usr/bin/../lib/gcc/x86_64-linux-gnu/7.4.0/../../../../include/c++/7.4.0/bits/stl_numeric.h:154:11
    #2 0x55a8b66aeecf in AnalyzePSBT(PartiallySignedTransaction) src/node/psbt.cpp:80:27
    #3 0x55a8b5db1a17 in test_one_input(std::vector<unsigned char, std::allocator<unsigned char> > const&) src/test/fuzz/psbt.cpp:28:35
…

$ src/test/fuzz/psbt
…
policy/feerate.cpp:18:34: runtime error: signed integer overflow: -7497025602362688435 * 1000 cannot be represented in type 'long'
    #0 0x5587f480b863 in CFeeRate::CFeeRate(long const&, unsigned long) src/policy/feerate.cpp:18:34
    #1 0x5587f327051f in AnalyzePSBT(PartiallySignedTransaction) src/node/psbt.cpp:116:22
    #2 0x5587f2971ac7 in test_one_input(std::vector<unsigned char, std::allocator<unsigned char> > const&) src/test/fuzz/psbt.cpp:28:35
…
```
"\nHint: Use gettransaction for wallet transactions.\n"
                "\nIf verbose is 'true', returns an Object with information about 'txid'.\n"
                "If verbose is 'false' or omitted, returns a string that is serialized, hex-encoded data for 'txid'.\n",
                {
                    {"txid", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The transaction id"},
                    {"verbose", RPCArg::Type::BOOL,  "false", "If false, return a string, otherwise return a json object"},
                    {"blockhash", RPCArg::Type::STR_HEX, RPCArg::Optional::OMITTED_NAMED_ARG, "The block in which to look for the transaction"},
                },
                {
                    RPCResult{"if verbose is not set or set to false",
            "\"data\"      (string) The serialized, hex-encoded data for 'txid'\n"
                     },
                     RPCResult{"if verbose is set to true",
            "{\n"
            "  \"in_active_chain\": b, (bool) Whether specified block is in the active chain or not (only present with explicit \"blockhash\" argument)\n"
            "  \"hex\" : \"data\",       (string) The serialized, hex-encoded data for 'txid'\n"
            "  \"txid\" : \"id\",        (string) The transaction id (same as provided)\n"
            "  \"hash\" : \"id\",        (string) The transaction hash (differs from txid for witness transactions)\n"
            "  \"size\" : n,             (numeric) The serialized transaction size\n"
            "  \"vsize\" : n,            (numeric) The virtual transaction size (differs from size for witness transactions)\n"
            "  \"weight\" : n,           (numeric) The transaction's weight (between vsize*4-3 and vsize*4)\n"
            "  \"version\" : n,          (numeric) The version\n"
            "  \"locktime\" : ttt,       (numeric) The lock time\n"
            "  \"vin\" : [               (array of json objects)\n"
            "     {\n"
            "       \"txid\": \"id\",    (string) The transaction id\n"
            "       \"vout\": n,         (numeric) \n"
            "       \"scriptSig\": {     (json object) The script\n"
            "         \"asm\": \"asm\",  (string) asm\n"
            "         \"hex\": \"hex\"   (string) hex\n"