Zeiss CZI: fix image reading for linescan images
Cellworx: fix off-by-one if all pixels files are missing

This won't allow .htd files without TIFFs to import, but it makes the
exception that is thrown more informative.

Fixes #6332.
fix link to Java Image I/O guide

current Bio-Formats minimum requirement is Java 6
Merge pull request #800 from melissalinkert/cellworx-off-by-1

Cellworx: fix off-by-one if all pixels files are missing
Merge pull request #797 from melissalinkert/czi-linescan-image

Zeiss CZI: fix image reading for linescan images
Merge pull request #801 from mtbc/java-imageio-link

fix link to Java Image I/O guide