ND2: only adjust for {Frame,Time}{Before,After} if LoopSize is used

Fixes #11997.
ND2: do not skip bytes at the end of text info blocks

Fixes #11873.
DICOM: correct units for physical sizes

Fixes #12307.
Leica LIF: do not set Channel.Color for RGB images

The stored color will usually (always?) be 0xffffffff, which causes the
displayed colors to be inaccurate (since the 'R' component will be shown
as white).

Fixes #12214.
OME-TIFF: close helper readers when working with single-plane files

The reader will be left open if only a tile was read, but if the full
plane from a single plane file is read then the helper reader will be
closed.  This reduces the memory usage for datasets that consist of many
single plane files.

Fixes #12219.
Change file closing check to look for lower-right-most tile
Merge pull request #1178 from melissalinkert/rebased/develop/nd2-part-2

Nikon .nd2 fixes, part 2 (rebased onto develop)
Merge pull request #1195 from melissalinkert/rebased/develop/12219

OME-TIFF: close helper readers when working with single-plane files (rebased onto develop)
Merge pull request #1192 from melissalinkert/12307

DICOM: fix units for physical sizes
Merge pull request #1193 from melissalinkert/12214

Leica LIF: do not set Channel.Color for RGB images