As seen in ooo95711-1.odt, the ODF import may create a redline that
starts on a SwTableNode - though i haven't been able to figure out how
such an odd creature might arise from UI actions.

Try to fix the obvious places so we don't crash easily; there might be
more trouble elsewhere though with code that assumes that a redline
starts on a SwTextNode.

Change-Id: I8431c1416ac4503ff0209a946398656f1c28366d