Fix hash_array

Commit a3d2b1bbe9 neglected to
initialize the type_id field of the synthesized type cache entry, so
it would make a new one on every call.

Also, better use the per-function memory context for this; otherwise
it leaks memory.

Discussion: https://www.postgresql.org/message-id/flat/17158-8a2ba823982537a4%40postgresql.org

src/backend/utils/adt/arrayfuncs.c

@@ -3992,13 +3992,14 @@ hash_array(PG_FUNCTION_ARGS)
 			MemoryContext oldcontext;
 			TypeCacheEntry *record_typentry;
 
-			oldcontext = MemoryContextSwitchTo(CacheMemoryContext);
+			oldcontext = MemoryContextSwitchTo(fcinfo->flinfo->fn_mcxt);
 
 			/*
 			 * Make fake type cache entry structure.  Note that we can't just
 			 * modify typentry, since that points directly into the type cache.
 			 */
-			record_typentry = palloc(sizeof(*record_typentry));
+			record_typentry = palloc0(sizeof(*record_typentry));
+			record_typentry->type_id = element_type;
 
 			/* fill in what we need below */
 			record_typentry->typlen = typentry->typlen;