Pictures typically have a single RTF group, so we imported them at the
end of that group. Though multiple inner groups are also allowed, so
make sure we only do the import at the very end, instead of at the end
of all inner groups as well, resulting in multiple (fake) pictures.

Regression from 13c00ce3 (Enable the
writerfilter-based RTF import in non-experimental mode, 2011-08-18).

Change-Id: Id895b2c6d3b824d09d89bfa01ce59aba76c55d42