(bug 44807) Don't crash on interwiki pages

e.g. /en/Wikt:Lede, which was the bug's example. It now returns a 404 error
with an indication of where you can get the actual page (but not in any
computer-readable format).

Change-Id: I88d27fe9af124c1bf06b90a54a4c9ee695564f79
Merge "(bug 44807) Don't crash on interwiki pages"