[Acquisition] Ensure that the bitDepth_ field is properly initialized.

Manual acquisitions could potentially leave this value at 0, which causes
weird display bugs and a potential EDT hang when the histograms are interacted
with.

git-svn-id: https://valelab.ucsf.edu/svn/micromanager2/trunk@14829 d0ab736e-dc22-4aeb-8dc9-08def0aa14fd