fix crash loading ooo#93570-3.doc

regression from f2945255df273404ee2457dcf761cb8f334b732b
cp#2013101510000026: doc import of comments affecting more text nodes

use Move(fnMoveBackward, fnGoNode) to at least ensure we stop going
backwards when we run out of valid places to go backwards to.

This still isn't great because the distance between two msword character
indexes only equates to the same distance between our characters in the very
simple cases

Change-Id: I248fd12c067577d2f1fd64f48583321eb6d453e4
coverity#704523 Division or modulo by zero

Change-Id: I165687b22f70a03d4bcb669a04d3495454d09042
coverity#706504 Uncaught exception

Change-Id: I727779317672fe58c440aee76762d0a9ae28d8ca
coverity#706055 Unintended sign extension

Change-Id: Ie917cfd5f41a6f5e58a4c629a6a5b800e2e0b42f
coverity#706056 Unintended sign extension

Change-Id: Iafb36f8135893186710ae3a939e50596a372d065
coverity#706065 Unintended sign extension

Change-Id: If482c75af5128778a176c40e38000b78f2087131
coverity#706073 Unintended sign extension

Change-Id: I13272490bf8a08cbfb1ffc37828fb30fb92f9139