Fix crash if we remove a tag when we're playing the animation

src/app/ui/editor/play_state.cpp

@@ -192,6 +192,8 @@ void PlayState::onRemoveTag(Editor* editor, doc::Tag* tag)
 {
   if (m_tag == tag)
     m_tag = nullptr;
+
+  m_playback.removeReferencesToTag(tag);
 }
 
 void PlayState::onPlaybackTick()

src/doc/playback.cpp

@@ -10,6 +10,7 @@
 
 #include "doc/playback.h"
 
+#include "base/remove_from_container.h"
 #include "doc/frame.h"
 #include "doc/sprite.h"
 #include "doc/tag.h"
@@ -144,6 +145,20 @@ Tag* Playback::tag() const
   return (!m_playing.empty() ? const_cast<Tag*>(m_playing.back()->tag): nullptr);
 }
 
+void Playback::removeReferencesToTag(Tag* tag)
+{
+  base::remove_from_container(m_tags, tag);
+  base::remove_from_container(m_played, tag);
+
+  for (auto it=m_playing.begin(); it!=m_playing.end(); ) {
+    std::unique_ptr<PlayTag>& playTag = *it;
+    if (playTag->tag == tag)
+      it = m_playing.erase(it);
+    else
+      ++it;
+  }
+}
+
 void Playback::handleEnterFrame(const frame_t frameDelta, const bool firstTime)
 {
   PLAY_TRACE("    handleEnterFrame", m_frame, "+", frameDelta);

src/doc/playback.h

@@ -76,6 +76,10 @@ namespace doc {
     // The tag that is being played right now (can be nullptr).
     Tag* tag() const;
 
+    // Should be called when a specific tag is going to be deleted so
+    // we remove all references to this tag.
+    void removeReferencesToTag(Tag* tag);
+
   private:
     // Information about playing tags (and inner tags)
     struct PlayTag {