Fix bug in the new ResourceOwner implementation.

When the hash table is in use, ResoureOwnerSort() moves any elements
from the small fixed-size array to the hash table, and sorts it. When
the hash table is not in use, it sorts the elements in the small
fixed-size array directly. However, ResourceOwnerSort() and
ResourceOwnerReleaseAll() had different idea on when the hash table is
in use: ResourceOwnerSort() checked owner->nhash != 0, and
ResourceOwnerReleaseAll() checked owner->hash != NULL. If the hash
table was allocated but was currently empty, you hit an assertion
failure.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://www.postgresql.org/message-id/be58d565-9e95-d417-4e47-f6bd408dea4b@gmail.com

Author: hlinnaka

src/backend/utils/resowner/resowner.c

@@ -349,10 +349,13 @@ ResourceOwnerReleaseAll(ResourceOwner owner, ResourceReleasePhase phase,
 	ResourceElem *items;
 	uint32		nitems;
 
-	/* ResourceOwnerSort must've been called already */
+	/*
+	 * ResourceOwnerSort must've been called already.  All the resources are
+	 * either in the array or the hash.
+	 */
 	Assert(owner->releasing);
 	Assert(owner->sorted);
-	if (!owner->hash)
+	if (owner->nhash == 0)
 	{
 		items = owner->arr;
 		nitems = owner->narr;
@@ -393,7 +396,7 @@ ResourceOwnerReleaseAll(ResourceOwner owner, ResourceReleasePhase phase,
 		kind->ReleaseResource(value);
 		nitems--;
 	}
-	if (!owner->hash)
+	if (owner->nhash == 0)
 		owner->narr = nitems;
 	else
 		owner->nhash = nitems;