pageinspect: Fix use of wrong memory context by hash_page_items.

This can cause it to produce incorrect output.

Report and patch by Masahiko Sawada.

Discussion: http://postgr.es/m/CAD21AoBc5Asx7pXdUWu6NqU_g=Ysn95EGL9SMeYhLLduYoO_OA@mail.gmail.com

contrib/pageinspect/hashfuncs.c

@@ -313,10 +313,10 @@ hash_page_items(PG_FUNCTION_ARGS)
 
 		fctx = SRF_FIRSTCALL_INIT();
 
-		page = verify_hash_page(raw_page, LH_BUCKET_PAGE | LH_OVERFLOW_PAGE);
-
 		mctx = MemoryContextSwitchTo(fctx->multi_call_memory_ctx);
 
+		page = verify_hash_page(raw_page, LH_BUCKET_PAGE | LH_OVERFLOW_PAGE);
+
 		uargs = palloc(sizeof(struct user_args));
 
 		uargs->page = page;