Add assertion to error path in streams.c (#15027)

This makes the developer intent clear and should prevent some false
reports.

main/streams/streams.c

@@ -2211,6 +2211,7 @@ PHPAPI php_stream *_php_stream_open_wrapper_ex(const char *path, const char *mod
 			options &= ~USE_PATH;
 		}
 		if (EG(exception)) {
+			ZEND_ASSERT(resolved_path == NULL);
 			return NULL;
 		}
 	}