If MC handler is connected but MC not available, the InitOK() flag is consistently...

If MC handler is connected but MC not available, the InitOK() flag is consistently set and the MCEvent() returns null, so the user tasks can rely on the MCEvent() to detect the availability of MC. By default the MC candler will now work in particle preload mode for efficiency reasons. User tasks get executed even if the MC handler was requested while no MC data, so the user code should consistently check for the fMCEvent pointer