D6856: Reset url in closeUrl()

[Elvis Angelaccio]

elvisangelaccio added a dependent revision: D6889: TestPart: add more test 
cases.

REVISION DETAIL
  https://phabricator.kde.org/D6856

To: elvisangelaccio, dfaure, #ktexteditor, #kate, #kdevelop
Cc: cullmann, #frameworks