Fix EmptyPage exception

Messagelog was throwing an EmptyPage exception when rendering its table using djangotables2.

Changed template to not try to generate a link to previous or next page when there's not one.

Branch: fix/emptypage-exception
Merge branch 'release-0.12.0' into fix/emptypage-exception

Branch: fix/emptypage-exception
Merge pull request #284 from rapidsms/fix/emptypage-exception

Fix EmptyPage exception