SVS: prevent NPE during type checking
Metamorph: prevent reading beyond the end of the file
TiffParser: prevent reading beyond the end of the file
OME-TIFF: prevent NPE during type checking
TIFF: sanitize image descriptions
Metamorph: prevent NPE on missing TIFF comment
Merge pull request #607 from melissalinkert/rebased/dev_4_4/tiff-fixes

Minor defensive programming changes for TIFF-based formats (rebased onto dev_4_4)