fdo#36329: Fix crash reading some documents with fields
fdo#36329: Fix crash reading some documents with fields

The problem came from the unsigned integer positions... Needed to
prevent the end position to get -1/max value.

Signed-off-by: Petr Mladek <9cbcfb1260d253e26a699647bd9cbee55818ea4a@suse.cz>
Signed-off-by: Tor Lillqvist <d7e1c1a966af497a2abd6e0cf00cbb63dd0496e4@novell.com>
Signed-off-by: Michael Meeks <7e3f212bc57cabc465c9df7f45a34ee84553965e@novell.com>

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core