only allow splitting clips

app/widget/timelinewidget/timelinewidget.cpp

@@ -362,7 +362,7 @@ void TimelineWidget::SplitAtPlayhead()
   foreach (TrackOutput* track, timeline_node_->Tracks()) {
     Block* b = track->BlockContainingTime(playhead_time);
 
-    if (b) {
+    if (b && b->type() == Block::kClip) {
       bool selected = false;
 
       // See if this block is selected

app/widget/timelinewidget/tool/razor.cpp

@@ -67,6 +67,7 @@ void TimelineWidget::RazorTool::MouseRelease(TimelineViewMouseEvent *event)
 
     // Ensure there's a valid block here
     if (block_at_time
+        && block_at_time->type() == Block::kClip
         && !blocks_to_split.contains(block_at_time)) {
       blocks_to_split.append(block_at_time);
 

app/widget/timelinewidget/undo/undo.cpp

@@ -351,7 +351,7 @@ BlockSplitCommand::BlockSplitCommand(TrackOutput* track, Block *block, rational
   old_length_(block->length()),
   point_(point)
 {
-  Q_ASSERT(point > block_->in() && point < block_->out());
+  Q_ASSERT(point > block_->in() && point < block_->out() && block_->type() == Block::kClip);
 
   // Ensures that this block is deleted if this action is undone
   new_block_ = static_cast<Block*>(block_->copy());