GUI: fix ins 0 being inserted on blank song

TODO.md

@@ -21,7 +21,6 @@
 - ability to customize startup system
 - store system presets in new file
 - Game Boy envelope macro/sequence
-- Game Boy envelope view
 - option to display chip names instead of "multi-system" on title bar
 - rewrite the system name detection function anyway
 - add nightly.link

src/gui/gui.cpp

@@ -915,6 +915,7 @@ void FurnaceGUI::noteInput(int num, int key, int vol) {
     }
     pat->data[cursor.y][1]=(unsigned char)pat->data[cursor.y][1];
     if (latchIns==-2) {
+      if (curIns>=(int)e->song.ins.size()) curIns=-1;
       pat->data[cursor.y][2]=curIns;
     } else if (latchIns!=-1 && !e->song.ins.empty()) {
       pat->data[cursor.y][2]=MIN(((int)e->song.ins.size())-1,latchIns);