When two (or more) text frames was imported without a non-frame
paragraph in between, the first frame was anchored to the second one,
instead of a non-frame paragraph.

The fix is modelled after what the old RTF import already did in
SwRTFParser::Continue() in swparrtf.cxx:493 and
SwRTFParser::SetFlysInDoc() in rtffly.cxx:481.