tdf#107877: Don't crash if all bitmaps are deleted

Change-Id: Ie21f8cf1ead7c75017ee09436102f87f5d5dc04c
Reviewed-on: https://gerrit.libreoffice.org/37673Reviewed-by: Julien Nabet <serval2412@yahoo.fr>
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>

cui/source/tabpages/tpbitmap.cxx

@@ -525,6 +525,8 @@ IMPL_LINK_NOARG(SvxBitmapTabPage, ModifyBitmapHdl, ValueSet*, void)
         }
     }
 
+    if(pGraphicObject)
+    {
         BitmapEx aBmpEx(pGraphicObject->GetGraphic().GetBitmapEx());
         Size aTempBitmapSize = aBmpEx.GetSizePixel();
         const double fUIScale = ( (mpView && mpView->GetModel()) ? double(mpView->GetModel()->GetUIScale()) : 1.0);
@@ -540,6 +542,12 @@ IMPL_LINK_NOARG(SvxBitmapTabPage, ModifyBitmapHdl, ValueSet*, void)
 
         m_pCtlBitmapPreview->SetAttributes( m_aXFillAttr.GetItemSet() );
         m_pCtlBitmapPreview->Invalidate();
+    }
+    else
+    {
+        SAL_WARN("cui.tabpages", "SvxBitmapTabPage::ModifyBitmapHdl(): null pGraphicObject");
+    }
+
 }
 
 IMPL_LINK_NOARG(SvxBitmapTabPage, ClickRenameHdl, SvxPresetListBox*, void)