Fix awaitFrames waiting for one frame too few

Since onFrame is based on a MutableStateFlow, there is
always the current value delivered first.

This is intended for `awaitCondition`, since this should complete
immediately if the condition is already met. As a consequence,
awaitFrames needs to wait for `count + 1` frames

Flag: TEST_ONLY
Bug: 389637975
Test: existing unit tests
Change-Id: I491cdeeda0d6425c90318bbfa38484eec494f4ee