Only add a MetadataOnly element if no TiffData elements are present

This prevents validation errors for most OME-TIFF files; noticed by @qidane.
merge dev_5_0 -D org: PR 998 (Micromanager fixes)
merge dev_5_0 -D org: PR 1024 (DICOM: fix file grouping so that path names are normalized)
merge dev_5_0 -D org: PR 1033 (Add the series index to the default image name)
merge dev_5_0 -D org: PR 1040 (Only add a MetadataOnly element if no TiffData elements are present (rebased onto dev_5_0))
merge dev_5_0 -D org

Repository: openmicroscopy/bioformats
Excluded PRs:
  # PR 1045 imunro 'Changes to ensure pmtMarker is read correctly.' (status: pending)
  # PR 1018 melissalinkert 'Flex: fix support for new file naming scheme' (status: pending)
  # PR 1016 ctrueden 'Use pom-scijava as parent' (label: exclude)
Already up-to-date.

Merged PRs:
  # PR 998 melissalinkert 'Micromanager fixes'
  # PR 1024 melissalinkert 'DICOM: fix file grouping so that path names are normalized'
  # PR 1033 melissalinkert 'Add the series index to the default image name'
  # PR 1040 melissalinkert 'Only add a MetadataOnly element if no TiffData elements are present (rebased onto dev_5_0)'

Generated by BIOFORMATS-5.0-merge-daily#791 (http://ci.openmicroscopy.org/job/BIOFORMATS-5.0-merge-daily/791/)