svx lok: fix crash on select all when there is no mpMarkedObj yet

Fixes the online.git HTTPWSTest::testRenderShapeSelectionImpress()
testcase by reverting one hunk of commit
3fb298f6 (lok: writer: svg export
transformed images, 2019-03-26).

This was probably meant to be a cleanup, but getting the sdr mark,
followed by getting the sdr object of the mark always gives us a shape,
while directly accessing mpMarkedObj does not.

Change-Id: Id733ba5c6fdf6fc86a3e9f7de62b4bdcbf9b06db
Reviewed-on: https://gerrit.libreoffice.org/72039Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>

svx/source/svdraw/svdmrkv.cxx

@@ -862,7 +862,8 @@ void SdrMarkView::SetMarkHandles(SfxViewShell* pOtherShell)
         {
             if (GetMarkedObjectCount())
             {
-                SdrObject* pO = mpMarkedObj;
+                SdrMark* pM = GetSdrMarkByIndex(0);
+                SdrObject* pO = pM->GetMarkedSdrObj();
                 long nRotAngle = pO->GetRotateAngle();
                 // true if we are delaing with a RotGrfFlyFrame
                 // (SwVirtFlyDrawObj with a SwGrfNode)