Gracefully handle non-ascii hrefs in redlinker

Title::newFromText() requires its input to be urldecoded, but the
redlinker was not decoding it before trying to generate the new title.

Fixes T78090

Bug: T78090
Change-Id: I5c79a1aadb65a1499f210265e02f8b04a1691d0f
(cherry picked from commit 0bac08ec24a1833fb395750130cd009d9f5cae2c)