<!-- Describe the issue -->

When our chainstate activation sequence fails and we're running the GUI, we ask the user via a question box whether or not they'd like to re-run the sequence with `fReindex = true`. Fun fact: despite the fact that this sequence is wrapped in a while loop, we only run it twice at most.

https://github.com/bitcoin/bitcoin/blob/7ecb309c4ed1bb9ae6b9a12cbb4f083328edc125/src/init.cpp#L1539-L1556

If they answer yes, the sequence will always fail, because a chainstate will have already been initialized in the original run and `InitializeChainstate` will throw a `std::logic_error`:

https://github.com/bitcoin/bitcoin/blob/7ecb309c4ed1bb9ae6b9a12cbb4f083328edc125/src/validation.cpp#L4573-L4594

This always reproduces. To reproduce:
```
gdb ./src/qt/bitcoin-qt
(gdb) b InitializeChainstate
(gdb) # add breakpoint for the "if (!fLoaded && !ShutdownRequested()) {" line
(gdb) r  # should stop at the breakpoint for InitializeChainstate
(gdb) c  # to advance to the breakpoint for the "if (!fLoaded && !ShutdownRequested()) {" line
(gdb) set fLoaded=false
(gdb) c  # should stop at the breakpoint for InitializeChainstate
(gdb) n  # step through InitializeChainstate to see that it throws
```

We expect the re-run of the chainstate activation sequence to not always fail.

INIT_REINDEX,
    INIT_DOWNLOAD,
    POST_INIT
};
extern RecursiveMutex cs_main;
extern Mutex g_best_block_mutex;
extern std::condition_variable g_best_block_cv;
extern uint256 g_best_block;
/** Whether there are dedicated script-checking threads running.
 * False indicates all script checking is done on the main threadMessageHandler thread.
 */
extern bool g_parallel_script_checks;
extern bool fRequireStandard;
extern bool fCheckBlockIndex;
extern bool fCheckpointsEnabled;
extern CFeeRate minRelayTxFee;
extern int64_t nMaxTipAge;
extern uint256 hashAssumeValid;
extern arith_uint256 nMinimumChainWork;
extern const std::vector<std::string> CHECKLEVEL_DOC;
void UnloadBlockIndex(CTxMemPool* mempool, ChainstateManager& chainman) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
void StartScriptCheckWorkerThreads(int threads_num);
void StopScriptCheckWorkerThreads();