No debugging unless the game is running

src/emulator.rs

@@ -305,6 +305,10 @@ impl Emulator {
     }
 
     fn start_debugging(&mut self, sim_id: SimId, sender: DebugSender) {
+        if self.sim_state[sim_id.to_index()].load(Ordering::Acquire) != SimState::Ready {
+            // Can't debug unless a game is connected
+            return;
+        }
         let debug = DebugInfo {
             sender,
             stop_reason: Some(DebugStopReason::Trapped),