[PATCH] Fix out-of-bouds access (src/common/wchar.c)

Hi,

Per Coverity.

Like the function pg_encoding_max_length_sql
(src/backend/utils/mb/mbutils.c)
Only assertion is insufficient to avoid accessing array out-of-bounds.

This bug is live according Coverity at function: pg_verify_mbstr_len
(src/backend/utils/mb/mbutils.c)
CID 1469870 (#1 of 1): Out-of-bounds access (OVERRUN)7. overrun-call:
Overrunning
callee's array of size 42 by passing argument src_encoding (which evaluates
to 63) in call to pg_verify_mbstr_len. [show details
<https://scan6.scan.coverity.com/eventId=32693869-7&modelId=32693869-0&fileInstanceId=131415642&filePath=%2Fdll%2Fpostgres%2Fpostgres%2Fsrc%2Fbackend%2Futils%2Fmb%2Fmbutils.c&fileStart=1546&fileEnd=1605>
]
633 retval = pg_verify_mbstr_len(src_encoding, src_str, len, false);
634

Trivial patch attached.

regards,

Ranier Vilela