[PATCH] Dereference null return value (NULL_RETURNS) (src/backend/commands/statscmds.c)

Hi Tom,

Per Coverity.

The SearchSysCache1 allows return NULL and at function AlterStatistics,
has one mistake, lack of, check of return, which enables a dereference NULL
pointer,
at function heap_modify_tuple.

While there is room for improvement.
Avoid calling SearchSysCache1 and table_open if the user "is not the owner
of the existing statistics object".

regards,
Ranier Vilela