QObject: Actually check unnormalized method signature

This was broken in f95181c7bb,
and has been broken in all released versions of Qt5.

Change-Id: Ia75ab602be4904cc6ab19471f909716538af8746
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>

src/corelib/kernel/qobject.cpp

@@ -2658,8 +2658,8 @@ QMetaObject::Connection QObject::connect(const QObject *sender, const char *sign
     const char *method_arg = method;
     ++method; // skip code
 
-    QByteArray methodName;
     QArgumentTypeArray methodTypes;
+    QByteArray methodName = QMetaObjectPrivate::decodeMethodSignature(method, methodTypes);
     const QMetaObject *rmeta = receiver->metaObject();
     int method_index_relative = -1;
     Q_ASSERT(QMetaObjectPrivate::get(rmeta)->revision >= 7);