The capture module had two entry points for doing pre-capture checks: one when a new sequence is started and one for continuing to capture within a sequence. This creates several problems and unexpected behaviour. For example, focusing and dithering did only work for continuing a sequence.
With this diff, both starting a new sequence and continuing a sequence runs through the same check before starting to capture a new frame.
All changes are related to light frames only, capturing darks, bias and flat frames is (hopefully) untouched.