X11: Don't call any X11 functions on fatal error

If X11 functions are called after a fatal error then it just triggers the fatal
error handler again eventually leading to stack overflow.

src/arch/LowLevelWindow/LowLevelWindow_X11.cpp

@@ -92,6 +92,9 @@ LowLevelWindow_X11::LowLevelWindow_X11()
 
 LowLevelWindow_X11::~LowLevelWindow_X11()
 {
+	if( FatalError )
+		return;
+
 	// Reset the display
 	if( !m_bWasWindowed )
 	{