tdf#109052: Crash after PPT import when undo is disabled

It was not a good idea to enable undo unconditionally.
Use the saved undo state instead.

Change-Id: I60875da23466b6ef54f034b447d636bdbab38151
Reviewed-on: https://gerrit.libreoffice.org/41823Reviewed-by: Tamás Zolnai <tamas.zolnai@collabora.com>
Tested-by: Tamás Zolnai <tamas.zolnai@collabora.com>

sd/source/filter/ppt/pptin.cxx

@@ -239,6 +239,7 @@ bool ImplSdPPTImport::Import()
         return false;
 
     pSdrModel->setLock(true);
+    const bool bSavedUndoEnabled = pSdrModel->IsUndoEnabled();
     pSdrModel->EnableUndo(false);
 
     SdrOutliner& rOutl = mpDoc->GetDrawOutliner();
@@ -1409,7 +1410,7 @@ bool ImplSdPPTImport::Import()
     xDocProps->setTemplateName(OUString());
 
     pSdrModel->setLock(false);
-    pSdrModel->EnableUndo(true);
+    pSdrModel->EnableUndo(bSavedUndoEnabled);
     return bOk;
 }