GUI: implement "clear all subsongs"

src/engine/engine.cpp

@@ -813,6 +813,16 @@ bool DivEngine::removeSubSong(int index) {
   return true;
 }
 
+void DivEngine::clearSubSongs() {
+  BUSY_BEGIN;
+  saveLock.lock();
+  song.clearSongData();
+  changeSong(0);
+  curOrder=0;
+  saveLock.unlock();
+  BUSY_END;
+}
+
 void DivEngine::changeSystem(int index, DivSystem which, bool preserveOrder) {
   int chanCount=chans;
   quitDispatch();

src/engine/engine.h

@@ -821,6 +821,9 @@ class DivEngine {
     // remove subsong
     bool removeSubSong(int index);
 
+    // clear all subsong data
+    void clearSubSongs();
+
     // change system
     void changeSystem(int index, DivSystem which, bool preserveOrder=true);
 

src/gui/gui.cpp

@@ -3494,10 +3494,7 @@ bool FurnaceGUI::loop() {
         case GUI_WARN_CLEAR:
           if (ImGui::Button("All subsongs")) {
             stop();
-            //e->lockEngine([this]() {
+            e->clearSubSongs();
-              //e->curSubSong->clearData();
-            //});
-            e->setOrder(0);
             curOrder=0;
             oldOrder=0;
             oldOrder1=0;