Fix missed ReleaseVariableStats() in intarray's _int_matchsel().

Fix missed ReleaseVariableStats() in intarray's _int_matchsel().

Given a WHERE clause like "int[] @@ query_int" or "query_int ~~ int[]"
where the query_int side is a table column having statistics,
_int_matchsel() exited without remembering to free the statistics
tuple.  This would typically lead to warnings about cache refcount
leakage, like
  WARNING:  resource was not closed: cache pg_statistic (73), tuple 42/12 has count 1
It's been wrong since this code was added, in commit c6fbe6d6f.

Bug: #19492
Reported-by: Man Zeng <zengman@halodbtech.com>
Author: Man Zeng <zengman@halodbtech.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/19492-ddcd0e22399ef85a@postgresql.org
Backpatch-through: 14