Fix issue of add/remove a frame at a scene before all key frames of a layer. When you added or removed a frame at a scene before all key frames of a layer, frameline was not updated correctly. It seems nothing happened, but domview is updated. This changeset fix this issue by correcting logic for boundary case.

<project>
	<scene src='list.mbsvg' />
	<source src='main.c'/>
	<source src='%n.c'/>
	<source src='%n.h'/>
	<source src='Makefile'/>
</project>