Change positioning on conversion of "text on path" back to text.

Uses the originalPath as an approximation of the new position instead of the bbox.

This is in response to inbox#491 (closed), where I tried to position text when there was no bbox (since it was entirely truncated by a short path or it was empty text). My solution meant that the text would land in different places if it was fully truncated or not. This makes it consistent.

It is untested on typical text, but this is a substantial deviation from current behaviour (albeit a minor UX issue) so posted.

Fixes inbox#491 (closed) (Crashfix deleting path with invisible text on path)
If this is too elaborate for the above fix I have an alternate commit from an alternative branch (nathanal/stopgap) that just sets the location at 0,0 for not visible text and calls it a day.