Switch to side-by-side view

--- a/ForgeWiki/forgewiki/wiki_main.py
+++ b/ForgeWiki/forgewiki/wiki_main.py
@@ -237,7 +237,8 @@
     def revert(self, version):
         require(has_artifact_access('edit', self.page))
         orig = self.get_version(version)
-        self.page.text = orig.text
+        if orig:
+            self.page.text = orig.text
         self.page.commit()
         redirect('.')