Fix project being broken.

- The commit 456d657ca9fb3da6bccd2445d58e4e5790697d2d broke the project
file by setting the OPFQuestionsViewController.xib to NULL.
- The bug showed itself when you tried to show the questions view, the
app would crash and complain that the xib file didn’t exist in the bundle.

Signed-off-by: Aron Cedercrantz <aron@cedercrantz.se>