Assertions in SwTextFrame::DestoryImpl that were added in
ee6eb7ab
are triggered when reproducing tdf#118690.

I've never liked these IsInDtor checks, so avoid the situation by
delaying the destruction of the temporary SwDoc.

Change-Id: I601da8b45e547f4903b7ff3b0c6461a01964f416
Reviewed-on: https://gerrit.libreoffice.org/60940Tested-by: Jan-Marek Glogowski <glogow@fbihome.de>
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>