removed pCaptionObj from accessibility

it was not initialized but accessed in one place. Checked with symphony code,
there was a set method which is not in AOO trunk, thus solved accesses to zero
pointer usage

(cherry picked from commit bd0c3b940f6006d3cb49381230795db667aeb943)

Conflicts:
	svx/inc/svx/svdobj.hxx
	svx/source/svdraw/svdobj.cxx

Change-Id: Ic8dec5c6def35753d757066c7ea02e1a92b46f6c