Special:PageLanguage: Show log extract only when title known

Special:PageLanguage: Show log extract only when title known

When open Special:PageLanguage without a page, the whole pagelang log is
shown and the notice:
Title::newFromText: $text must be a string. This will throw an
InvalidArgumentException in future. [Called from LogPager::limitTitle]
The whole log is useless at this position, so showing it only when
looking at a specific page.

Change-Id: I2a0b7ccc71789506554617e1d12797e72835a12a