Micromanager: use full channel name in file names when necessary

If the trimmed name (everything before the first '-') is not sufficient
for picking up TIFF files, then use the full channel name.  I suspect
this is only an issue for datasets produced with older versions of
Micromanager, but that may not be correct.
MM: trim the timepoint count if all files are missing beyond a certain point

Fixes ticket #11972.
Micromanager: do not allow Position to query reader state in openBytes

This prevents potential exceptions when openBytes is called on a
memoized file.
Merge pull request #998 from melissalinkert/micromanager

Micromanager fixes