Cocoa Port: Fix yet another crash-on-exit bug that could happen when running on an older system.

desmume/src/GPU.cpp

@@ -4763,6 +4763,13 @@ void GPUSubsystem::_UpdateFPSRender3D()
 
 void GPUSubsystem::SetEventHandler(GPUEventHandler *eventHandler)
 {
+	if ( (eventHandler == NULL) && (this->_event != this->_defaultEventHandler) )
+	{
+		this->ForceFrameStop();
+		this->_event = this->_defaultEventHandler;
+		return;
+	}
+	
 	this->_event = eventHandler;
 }
 

desmume/src/frontend/cocoa/cocoa_GPU.mm

@@ -193,6 +193,8 @@ GPU3DInterface *core3DList[GPU_3D_RENDERER_COUNT+1] = {
 
 - (void)dealloc
 {
+	GPU->SetEventHandler(NULL); // Unassigned our event handler before we delete it.
+	
 	delete fetchObject;
 	delete gpuEvent;