Change "blocking" BlockingLoop::Stop to give up and die after a timeout.

This fixes the global-static fifo object causing infinite hangs in some
cases. Notably, failure to initialize a graphics backend would result in
BlockingLoop::Prepare being called but never executing Run(), leaving the
object in a bad state.

Source/Core/VideoCommon/Fifo.cpp

@@ -144,7 +144,7 @@ void ExitGpuLoop()
 
   // Terminate GPU thread loop
   s_emu_running_state.Set();
-  s_gpu_mainloop.Stop(false);
+  s_gpu_mainloop.Stop(s_gpu_mainloop.kNonBlock);
 }
 
 void EmulatorState(bool running)