Check for stack overrun in standard_ProcessUtility().

ProcessUtility can recurse, and indeed can be driven to infinite
recursion, so it ought to have a check_stack_depth() call.  This
covers the reported bug (portal trying to execute itself) and a bunch
of other cases that could perhaps arise somewhere.

Per bug #15428 from Malthe Borch.  Back-patch to all supported branches.

Discussion: https://postgr.es/m/15428-b3c2915ec470b033@postgresql.org

src/backend/tcop/utility.c

@@ -332,6 +332,9 @@ standard_ProcessUtility(Node *parsetree,
 {
 	bool		isTopLevel = (context == PROCESS_UTILITY_TOPLEVEL);
 
+	/* This can recurse, so check for excessive recursion */
+	check_stack_depth();
+
 	check_xact_readonly(parsetree);
 
 	if (completionTag)