Make KernelState::TerminateTitle try to terminate XThreads safely.

src/xenia/kernel/kernel_state.h

@@ -142,6 +142,7 @@ class KernelState {
   }
 
   // Terminates a title: Unloads all modules, and kills all guest threads.
+  // This DOES NOT RETURN if called from a guest thread!
   void TerminateTitle(bool from_guest_thread = false);
 
   void RegisterThread(XThread* thread);