-keepnotewitnesscache -rescan -rescanheight with no blocks does a coredump #103

I ran into an issue and removed the blocks/ and chainstate/ directories inside my HUSH3 directory, which had a default autocreated wallet.dat. I had a script to start hushd which uses -keepnotewitnesscache -rescan -rescanheight and used that. hushd coredumped.

This is not high priority, as users will not normally do this, but hushd should not coredump in this situation. It should either sync normally or exit with an error that the CLI arguments were not valid.

This is the end of the debug.log:

2022-01-30 20:12:42 Initializing databases...
2022-01-30 20:12:42 init message: Verifying blocks...
2022-01-30 20:12:42 Verifying block DB... block index              16ms
2022-01-30 20:12:42 init message: Loading wallet...
2022-01-30 20:12:42 nFileVersion = 3090150
2022-01-30 20:12:42 Keys: 102 plaintext, 0 encrypted, 102 w/ metadata, 102 total
2022-01-30 20:12:42 ZKeys: 0 plaintext, 0 encrypted, 0 w/metadata, 0 total
2022-01-30 20:12:42  wallet                    5ms
2022-01-30 20:12:42 AppInit2: keeping NoteWitnessCache with rescan height=817463

This is the backtrace:

#0  AppInit2 (threadGroup=..., scheduler=...) at /usr/include/c++/8/bits/stl_vector.h:805
#1  0x000056453f1ca114 in AppInit (argc=<optimized out>, argv=<optimized out>) at bitcoind.cpp:238
#2  0x000056453f1b6a6f in main (argc=6, argv=0x7ffe5a88c368) at bitcoind.cpp:268

Looks like AppInit2 is potentially missing some error-checking to see if arguments are valid block heights the node knows about.