This reverts commit 9accbfa0.

... and the code change of "avoid crashing on load of fdo54724-1.rtf"
commit 4ee3eabd.

It's much simpler to detect early in convertToTable that there is a
row with no cells in it, which should not be allowed.

Change-Id: Iff6d235b29514edd57cc55addeefb24242595d88