pgsql: Fix missed case for builtin collation provider.

Fix missed case for builtin collation provider.

A missed check for the builtin collation provider could result in
falling through to call isalpha().

This does not appear to have practical consequences because it only
happens for characters in the ASCII range. Regardless, the builtin
provider should not be calling libc functions, so backpatch.

Discussion: https://postgr.es/m/1bd5a0a5192f82c22ee7527e825b18ab0028b2c7.camel@j-davis.com
Backpatch-through: 17

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/98c5b191e74b65b74149bb436b057d7007d401a7

Modified Files
--------------
src/backend/utils/adt/like_support.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)