SwTxtCursor::GetCrsrOfst nChgNode arg is only ever false/true

(resp. sal_False/True).  This was MSHORT, with the accompanying

  sal_Bool bChgNode = 1 < nChgNode;

check ever since 84a3db80b4fd66c6854b3135b5f69b61fd828e62 "initial import," but
there appear to be no calls that would pass in a value > 1, at least not on
recent master.

Change-Id: If87cb08ecfa665bbd54929d98d0c8de8286ae9ec