When using QtDbus as Out-of-Process IPC mechanism, arguments are not handled correctly in all cases

When using QtDbus as an IPC mechanism some methods types can not be called. For example the method:

ContextInfo ContextClient::contextTypeInfo(const QString& contextId) const

will not work, leading to a "can not be called" warning on the server side. It appears that only user-type arguments are considered during argument processing in the "int QServiceMetaObjectDBus::qt_metacall(QMetaObject::Call c, int id, void **a)" method. The first part of the attached patch is a hack that works around that issue.

Furthermore, in some cases (standard) return types appear to be ignored. For instance the following method:

RecordingInfoId ContextClient::addScheduledRecording(RecordingInfo recordinginfo);

leads to an "Internal error: Failed to deliver message" on the server side. Note that RecordingInfoId and QueryId are typedefs of QString so they are handled as standard return types. It seems that that QMetamethod::invoke(...) is called without the QGenericReturnArgument argument and hence the return value is not considered. The second and third part of the patch illustrate this. Obviously this is just a workaround for QString based return values and not suggested as a generic solution for this problem.