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.

<LEFT>		Turn to left.
<RIGHT>		Turn to right.
<UP>		Turn to up.
<DOWN>		Turn to down.
<SPACE>		To Fire.