Two fixes for certain lsm (zeiss) tiff images.

The first fix is that some zeiss images set PlanarConfig to "SEPARATE"
(i.e. separate color planes) even when NumberOfSamples is 1.  When the
number of samples is one, the PlanarConfig can be safely ignored.

The second fix is that ReadVolume assumed that the number of slices was
always equal to NumberOfPages, which was in conflict with ExecuteInformation
which set the number of slices to SubFiles if SubFiles > 0 (cf line 505).
This caused a crash, because ReadVolume was reading more data than the
reader had allocated space for.

Change-Id: I822e45a53c210b5edebfe8ce27443fe1434110ba