Fix incorrect placement of pfree() in pg_relation_check_pages()

This would cause the function to crash when more than one page is
considered as broken and reported in the SRF.

Reported-by: Noriyoshi Shinoda
Discussion: https://postgr.es/m/TU4PR8401MB11523D42C315AAF822E74275EE170@TU4PR8401MB1152.NAMPRD84.PROD.OUTLOOK.COM

src/backend/utils/adt/pagefuncs.c

@@ -220,10 +220,10 @@ check_relation_fork(TupleDesc tupdesc, Tuplestorestate *tupstore,
 
 		/* Save the corrupted blocks in the tuplestore. */
 		tuplestore_putvalues(tupstore, tupdesc, values, nulls);
-
-		pfree(path);
 	}
 
+	pfree(path);
+
 	/* Pop the error context stack */
 	error_context_stack = errcallback.previous;
 }