Don't hide unexpected errors in PyErr_WarnExplicitObject(). (#4585)

Python/ast.c

@@ -4160,9 +4160,9 @@ warn_invalid_escape_sequence(struct compiling *c, const node *n,
     }
     if (PyErr_WarnExplicitObject(PyExc_DeprecationWarning, msg,
                                    c->c_filename, LINENO(n),
-                                   NULL, NULL) < 0 &&
-        PyErr_ExceptionMatches(PyExc_DeprecationWarning))
+                                   NULL, NULL) < 0)
     {
+        if (PyErr_ExceptionMatches(PyExc_DeprecationWarning)) {
             const char *s;
 
             /* Replace the DeprecationWarning exception with a SyntaxError
@@ -4173,6 +4173,7 @@ warn_invalid_escape_sequence(struct compiling *c, const node *n,
             if (s != NULL) {
                 ast_error(c, n, s);
             }
+        }
         Py_DECREF(msg);
         return -1;
     }