sc: don't crash on loading comments

Seems filters call ShowNote before a view is set or something.
Fixup for 25555c50.

Change-Id: I9a69bf28b17cb16df7f1b1d06d9d3168da4a34b5
Reviewed-on: https://gerrit.libreoffice.org/46000Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
Tested-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>

sc/source/ui/docshell/docfunc.cxx

@@ -1216,7 +1216,8 @@ bool ScDocFunc::ShowNote( const ScAddress& rPos, bool bShow )
 
     ScTabView::OnLOKNoteStateChanged(pNote);
 
-    ScDocShell::GetViewData()->GetScDrawView()->SyncForGrid(pNote->GetCaption());
+    if (ScDocShell::GetViewData())
+        ScDocShell::GetViewData()->GetScDrawView()->SyncForGrid(pNote->GetCaption());
     rDocShell.SetDocumentModified();
 
     return true;