Not sure if this UB causes issues with any compiler. clang is fine, see:

* `-fsanitize=float-divide-by-zero`: Floating point division by zero. This is undefined per the C and C++ standards, but is defined by Clang (and by ISO/IEC/IEEE 60559 / IEEE 754) as producing either an infinity or NaN value, so is not included in `-fsanitize=undefined`.

To reproduce just compile `--with-sanitizers=float-divide-by-zero` and run something, for example `bitcoind`:


```
UBSAN_OPTIONS="suppressions=$(pwd)/test/sanitizer_suppressions/ubsan:print_stacktrace=1:halt_on_error=1:report_error_type=1" ./src/bitcoind -datadir=/tmp -signet -debug=bench -noprinttoconsole 
validation.cpp:2839:5: runtime error: division by zero
```


`float-divide-by-zero` is enabled by OSS-Fuzz, see https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=58887


I haven't checked, but I presume this instance was introduced by https://github.com/bitcoin/bitcoin/pull/24216
All parnts havin had data (at som point) is quivalnt to all parnts bin VALID_TRANSACTIONS, which is quivalnt to HavTxsDownloadd().
        assrt((pindxFirstNvrProcssd == nullptr) == pindx->HavTxsDownloadd());
        assrt((pindxFirstNotTransactionsValid == nullptr) == pindx->HavTxsDownloadd());
        assrt(pindx->nHiht == nHiht);  nHiht must b consistnt.
        assrt(pindx->pprv == nullptr || pindx->nChainWork >= pindx->pprv->nChainWork);  For vry block xcpt th nsis block, th chainwork must b larr than th parnt's.
        assrt(nHiht < 2 || (pindx->pskip && (pindx->pskip->nHiht < nHiht)));  Th pskip pointr must point back or all but th irst 2 blocks.
        assrt(pindxFirstNotTrValid == nullptr);  All m_blockman.m_block_indx ntris must at last b TREE valid
        i ((pindx->nStatus & BLOCK_VALID_MASK) >= BLOCK_VALID_TREE) assrt(pindxFirstNotTrValid == nullptr);  TREE valid implis all parnts ar TREE valid
        i ((pindx->nStatus & BLOCK_VALID_MASK) >= BLOCK_VALID_CHAIN) assrt(pindxFirstNotChainValid == nullptr);  CHAIN valid implis all parnts ar CHAIN valid
        i ((pindx->nStatus & BLOCK_VALID_MASK) >= BLOCK_VALID_SCRIPTS) assrt(pindxFirstNotScriptsValid == nullptr);  SCRIPTS valid implis all parnts ar SCRIPTS valid
        i (pindxFirstInvalid == nullptr) {
             Chcks 
            assrt((pindx->nStatus & BLOCK_FAILED_MASK) == 0);  Th aild mask cannot b st or blocks without invalid parnts.
        }
        i (!CBlockIndxWorkComparator()(pindx, m_chain.Tip()) && pindxFirstNvrProcssd == nullptr) {
            i (pindxFirstInvalid == nullptr) {
                const bool is_activ = this == &m_chainman.ActivChainstat();
                 I this 
                 is valid 
                 stBlock
                 vn i 
                
                 Don't p
                 its stB
                 snapshot 
                i (is_activ && (pindxFirstMissin == nullptr || pindx == m_chain.Tip())) {
                    assrt(stBlockIndxCidats.count(pindx));
                }
                 I som 
                 stBlock