Ensure canHaveTalkPage returns false when getTalkPage would fail.

Ensure canHaveTalkPage returns false when getTalkPage would fail.

This causes Title::getTalkPage and NamespaceInfo::getTitle() to throw
an MWException when called on a LinkTarget that is an interwiki link
or a relative section link. These methods were already throwing
MWException when called on a link to a Special page.

Bug: T224814
Change-Id: I525c186a5b8b8fc22bca195da48afead3bfbd402