Workaround for T111513

It is wasteful to interrupt the bot just because of an unsupported
interwiki link. Here, we only test if it *is* an interwiki link, then we
skip it whatever syntax it has. This error only confirms that.

Bug: T136280
Change-Id: If013e15e4282fd29ef6f0f81e8c6f984d7fde70e