BUG: add missing return statements when read fails - led to crash

ReadDataInternal is meant to return a status code indicating success
or failure, however some branches that generated error messages
neglected to return 0 meaning that the calling code interpreted
this as a success condition.  In some cases this led to a crash, for
example when importing RGB dicom files.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22868 3bd1e089-480b-0410-8dfb-8563597acbee