Zeiss CZI: fix dimension calculations when expected planes are missing (rebased onto dev_5_0)



This is the same as gh-1386 but rebased onto dev_5_0.

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This should fix http://trac.openmicroscopy.org.uk/ome/ticket/12556.  The dimensions for the files in QA 9521 and 10301 should now match the expected dimensions listed in the ticket and QA issues.  I would not expect this to cause any test failures.

/cc @emilroz