Buffer(Queue/State)Layer: Consolidate preparePerFrameCompositionState

The only difference is the BLAST implementation fails when there is
no cached buffer. While in general we expect cacheBuffers to be called
by apply() there's no reason to add more code just to fail here.
Noticed this while investigating a bug where cacheBuffers wasn't
called.

Bug: 153561718
Test: Existing tests pass
Change-Id: If1faae68ef11de3f8b37474abeff14c42af3cd57