pgsql: Fix over-optimistic caching in fetch_array_arg_replace_nulls().

Fix over-optimistic caching in fetch_array_arg_replace_nulls().

When I rewrote this in commit 56a79a869bedc4bf6c35853642694cc0b0594dd2,
I forgot that it's possible for the input array type to change from one
call to the next (this can happen when applying the function to
pg_statistic columns, for instance).  Fix that.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/77903ede08845e55bd2a6c99b52d8da6926d6e84

Modified Files
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src/backend/utils/adt/array_userfuncs.c |   36 +++++++++++++++++++------------
1 file changed, 22 insertions(+), 14 deletions(-)