tdf#114992: fix crash in deleting sheet

See bt:
https://bugs.documentfoundation.org/attachment.cgi?id=139087

Change-Id: Iee72385a8e5400436da72fe5e18b8cdfccad193d
Reviewed-on: https://gerrit.libreoffice.org/47850Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
(cherry picked from commit 1d71f886)
Reviewed-on: https://gerrit.libreoffice.org/47860Reviewed-by: Eike Rathke <erack@redhat.com>

sc/source/ui/view/tabvwshf.cxx

@@ -611,7 +611,7 @@ void ScTabViewShell::ExecuteTable( SfxRequest& rReq )
                                 {
                                     const ScDPObject& rDPObj = (*pDPs)[i];
                                     const ScSheetSourceDesc* pSheetSourceDesc = rDPObj.GetSheetDesc();
-                                    if (pSheetSourceDesc->GetSourceRange().aStart.Tab() == nSelTab)
+                                    if (pSheetSourceDesc && pSheetSourceDesc->GetSourceRange().aStart.Tab() == nSelTab)
                                         bTabWithPivotTable = true;
                                 }
                             }