Fix crash deleting a tag that is being played in the Preview window

Fix: https://community.aseprite.org/t/consistent-crashing-when-deleting-loop-tag/1984

src/app/ui/editor/editor.cpp

@@ -1950,6 +1950,8 @@ void Editor::onAddFrameTag(DocEvent& ev)
 void Editor::onRemoveFrameTag(DocEvent& ev)
 {
   m_tagFocusBand = -1;
+  if (m_state)
+    m_state->onRemoveFrameTag(this, ev.frameTag());
 }
 
 void Editor::setCursor(const gfx::Point& mouseScreenPos)

src/app/ui/editor/editor_state.h

@@ -22,6 +22,10 @@ namespace ui {
   class TouchMessage;
 }
 
+namespace doc {
+  class FrameTag;
+}
+
 namespace app {
   class Editor;
   class EditorDecorator;
@@ -117,6 +121,9 @@ namespace app {
     // Custom ink in this state.
     virtual tools::Ink* getStateInk() { return nullptr; }
 
+    // Called when a tag is deleted.
+    virtual void onRemoveFrameTag(Editor* editor, doc::FrameTag* tag) { }
+
   private:
     DISABLE_COPYING(EditorState);
   };

src/app/ui/editor/play_state.cpp

@@ -167,6 +167,12 @@ bool PlayState::onSetCursor(Editor* editor, const gfx::Point& mouseScreenPos)
   return true;
 }
 
+void PlayState::onRemoveFrameTag(Editor* editor, doc::FrameTag* tag)
+{
+  if (m_tag == tag)
+    m_tag = nullptr;
+}
+
 void PlayState::onPlaybackTick()
 {
   ASSERT(m_playTimer.isRunning());

src/app/ui/editor/play_state.h

@@ -35,6 +35,7 @@ namespace app {
     bool onKeyDown(Editor* editor, ui::KeyMessage* msg) override;
     bool onKeyUp(Editor* editor, ui::KeyMessage* msg) override;
     bool onSetCursor(Editor* editor, const gfx::Point& mouseScreenPos) override;
+    void onRemoveFrameTag(Editor* editor, doc::FrameTag* tag) override;
 
   private:
     void onPlaybackTick();