Leica LIF: fix support for new files with 0 padding

Fixes http://trac.openmicroscopy.org.uk/ome/ticket/12144.  With this change, files in ```leica-lif/fabrice/new```, ```leica-lif/ron/```, and QA 9457 should all open/import without throwing an exception, and there should be nothing obviously wrong with the images and metadata.

All other files should not be affected, so builds should remain green.