Fix return value

The method actually returns a boolean.

Change-Id: I5887ad23e19be9a9c87c7858d81891378fd23cc9
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/corelib/kernel/qobject.cpp

@@ -5179,7 +5179,7 @@ bool QObject::disconnectImpl(const QObject *sender, void **signal, const QObject
         }
         if (!senderMetaObject) {
             qWarning("QObject::disconnect: signal not found in %s", sender->metaObject()->className());
-            return QMetaObject::Connection(0);
+            return false;
         }
         signal_index += QMetaObjectPrivate::signalOffset(senderMetaObject);
     }