Fix a potential buffer overread in sqlite3VdbeRecordCompare() when a

Fix a potential buffer overread in sqlite3VdbeRecordCompare() when a
serial_type specifies a field that starts in bounds but is much too large
for the allocated buffer.  Mostly harmless.  The overread is unlikely to
go more than one or two bytes past the end of the buffer.

FossilOrigin-Name: e436b2f4e5c5e6b2f70e65332c0c7d618e2ef20a