Dragging code triggers project changed even if no change occurred (e.g. drag was cancelled)

[kchadha]

Expected Behavior

Dragging code but cancelling the action should not trigger "Save Now" to appear in the menu bar.

Actual Behavior

Dragging code always triggers a project changed state even if:

1. Dragging out of the toolbox and then cancelling the drag by moving the block back to the toolbox to delete it
2. Dragging a block from the toolbox directly to the backpack (no actual change occurred in the project)
3. Dragging a block from a sprite's workspace to some place that does not accept blocks (therefore effectively cancelling the drag)

This is possibly a tricky issue because of how scratch-blocks emits move/drag events.