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.

if X_BACKEND
SUBDIRS = calculator tank drag
if SH_TEXT
SUBDIRS += svg2code_ex dynamic menu
endif
endif