Default to "r" mode if IAdmin.canUpdate fails (Fix #10657)

Any call to `RawFileStore.setFileId` with omero.group set to -1
was failing with an InternalException because IAdmin.canUpdate
was throwing. With this change, RawFileBean assumes that if
canUpdate fails that the mode should be "r", meaning no changes
are permissible to the file. Callers will need to explicitly
change the group id for "rw" behavior.

The major concern with this solution is that the action is silent:
even the owner of the file if calling with "-1" will not be able
to make changes.
Merge pull request #1011 from joshmoore/10657-setFileId

Default to "r" mode if IAdmin.canUpdate fails (Fix #10657)