The QLibraryInfo::location() method returns paths with native
path separator. This results to an invalid url when the path
is added to url with file://.

In this commit the url is constructed from the local path using
QUrl::toEncoded() method, thus ensuring the path separators are
handled correctly.

Change-Id: Ied128fc6931a1763e71863d11762bb09ca251e1c
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>