[REVIEW 3.5 (and maybe 3.4?)] fdo#42771: Fix crash when loading an invalid .fodt

Hi,

We throw an uncatched exception:

https://bugs.freedesktop.org/show_bug.cgi?id=42771

The fix is here:

http://cgit.freedesktop.org/libreoffice/core/commit/?id=9951de4a10386a85dc1bfa465304cd0005414b8e

Returning a 'I was unable create a cursor' value via throwing runtime
exception [in SwXFootnote::createTextCursorByRange()] is not really
efficient ;-) - but I have no idea what I might break by changing that,
so I just catch the exception in the code that already somehow counts on
the possibility that the call fails anyway.  This way, the filter fails
nicely, with our "favorite" 'General Input/Output Error.'

Please approve for libreoffice-3-5, and for libreoffice-3-4 too, if it
applies there.

Thank you,
Kendy