QmlDesigner: bug fix for components

QLibraryInfo::location(QLibraryInfo::ImportsPath) might miss the '/'
at the end.

Change-Id: I552cef7efce7644fad82247850d8853c72edd0ea
Reviewed-on: http://codereview.qt-project.org/5150


Reviewed-by: Tim Jenssen <tim.jenssen@nokia.com>
Reviewed-by: Eike Ziller <eike.ziller@nokia.com>