DolphinQt: Only update call stack if paused

This avoids a pseudo infinite loop where CodeWidget::UpdateCallstack
would lock the CPU in order to read the call stack, causing the CPU to
call Host_UpdateDisasmDialog because it's transitioning from running to
pausing, causing Host::UpdateDisasmDialog to be emitted, causing
CodeWidget::Update to be called, once again causing
CodeWidget::UpdateCallstack to be called, repeating the cycle.

Dolphin didn't go completely unresponsive during this, because
Host_UpdateDisasmDialog schedules the emitting of Host::UpdateDisasmDialog
to happen on another thread without blocking, but it was stopping certain
operations like exiting emulation from working.

Source/Core/DolphinQt/Debugger/CodeWidget.cpp

@@ -322,11 +322,11 @@ void CodeWidget::Update()
 
 void CodeWidget::UpdateCallstack()
 {
-  if (Core::GetState() == Core::State::Starting)
-    return;
-
   m_callstack_list->clear();
 
+  if (Core::GetState() != Core::State::Paused)
+    return;
+
   std::vector<Dolphin_Debugger::CallstackEntry> stack;
 
   const bool success = [&stack] {