Fix yeiling error message when select a scene. - It is caused by the buggy fixing of changeset #7d700e5f82ba for an eariler error of frameline.get_frame_block() - Fix frameline.get_frame_block() with correct logic and fix early code relied on the buggy fix.

<project>
	<scene src="/tmp/scene.mbsvg"/>
	<scene src="/tmp/second.mbsvg"/>
	<source src="/tmp/main.c"/>
	<source src="/tmp/second.c"/>
</project>