Gatan: fix physical dimension parsing when the Z size is missing

Fixes #12478.
Deltavision: conditionally ignore stage positions values of 0

If only two unique positions are present in X and Y, and one of them is
0 in both cases, then we ignore the 0 positions (with the result being
that there is only one tile).  See gh-1320.
ND2: prevent NumberFormatExceptions when parsing text data
Merge pull request #1317 from melissalinkert/ticket-12478

Gatan: fix physical dimension parsing when the Z size is missing
Merge pull request #1324 from melissalinkert/dv-stages

Deltavision: conditionally ignore stage position values of 0
Merge pull request #1335 from melissalinkert/rebased/develop/ticket-12536

ND2: prevent NumberFormatExceptions when parsing text data (rebased onto develop)