Since we can't know the real SalLayoutGlyphsImpl type, we
always have to clone and delete it on assignemt and in the
copy constructor.

Change-Id: I3e3aa1e0271c5ecbb1474a70fae5e63bd7124677
Reviewed-on: https://gerrit.libreoffice.org/62583
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>