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



This is the same as gh-1291 but rebased onto develop.

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Fixes http://trac.openmicroscopy.org.uk/ome/ticket/12536.  To test, verify that the file from QA 9463 opens without throwing an exception.  There should be 201 Z sections and 3 channels, as in NIS Elements Viewer.