6984 changes cause SEGV

[Anduin Withers <awithers@…>]

MythContextPrivate::mainWidow is left uninitialized when ScreenSaverControl::get() is called. The subsequent ScreenSaverX11::ScreenSaverX11() call invokes myth_system, which tries to fetch the main window to send the lirc stop event to; an access to random memory is made, the result of which is occasionally unpleasant.

Stuart Auchterlonie posted a backtrace to the -dev list which I won't reproduce here as it is easy enough to generate.

[danielk]

(In [6986]) Closes #196.

Moving the screensaver stuff to Init() in [6984] did not fix the segmentation fault caused by [6977]. Looking deeper at the problem it looks like we need neither the lirc nor the joystick lock at that point. These are only needed once there is a MythMainWindow.

So this fix:

• Makes util.cpp only request the locks when there is a MythContext and it has a MythMainWindow.
• Adds a safety check for the existance of a MythContext in lock().
• Initializes all the variables in MythContextPrivate as early as possible; to make sure all pointers are initialized to NULL if they haven't been set yet.