Fix crash due to reverse selection.

Selection start can be bigger than selection end and this kind
of selection is generated by mouse selection at least from L MR1.

To fix and support SHARE button for this kind of selection,
getSelectedText need to invert selection start and selection end
when the selection start is bigger than selection end.

Bug: 22065979
Change-Id: Ide4ac41e3f59d256033aca004450712ca0bb0f03