When importing SdrObjCustomShape for each an Outliner and a
VirtualDevice as RefDevice are created and held. On 32bit systems this
breaks the import with many such objects (in the bugdoc around 4300). On
64bit it works, but more memory as necessary is used. To avoid this,
flush the UNO API implementations at these objects after one page is
imported.  Do not do this for each single object, that will break the
connector import which does some processing later.

Change-Id: I7296edd40f01c1a40258808d78bf39e6d4fe29bf
Reviewed-on: https://gerrit.libreoffice.org/19990Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
Tested-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>