fdo#71892: sw: fix crash when pasting table in footnote

The code that updates RSIDs assumes that the number of nodes copied is
the same as the number of nodes inserted, which is not true when pasting
a table into a footnote because Writer can't do that, hence all table
nodes are missing.  Count inserted nodes instead.

(regression from 062eaeffe7cb986255063bb9b0a5f3fb3fc8e34c)

(cherry picked from commit 4580094d2d9d5b952c4526ee23204f75a5bb2f1b)

Conflicts:
	sw/source/core/frmedt/fecopy.cxx

(cherry picked from commit 2171fff4c1a57ede8f9693d7c0d95c1171a49a70)

Change-Id: I77b5b7751d1036a6401f708532537d874969502e
Reviewed-on: https://gerrit.libreoffice.org/6951
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>