Fix another raise-before-stealing-argument bug

src/runtime/dict.cpp

@@ -48,6 +48,17 @@ static void _dictSetStolen(BoxedDict* self, BoxAndHash k, STOLEN(Box*) v) {
     }
 }
 
+static void _dictSetStolen(BoxedDict* self, Box* k, STOLEN(Box*) v) {
+    BoxAndHash hashed_key;
+    try {
+        hashed_key = BoxAndHash(k);
+    } catch (ExcInfo e) {
+        Py_DECREF(v);
+        throw e;
+    }
+    return _dictSetStolen(self, hashed_key, v);
+}
+
 static void _dictSet(BoxedDict* self, BoxAndHash k, Box* v) {
     _dictSetStolen(self, k, incref(v));
 }

src/runtime/types.h

@@ -920,6 +920,7 @@ struct BoxAndHash {
     Box* value;
     size_t hash;
 
+    BoxAndHash() {}
     BoxAndHash(Box* value) : value(value), hash(PyHasher()(value)) {}
     BoxAndHash(Box* value, size_t hash) : value(value), hash(hash) {}