D27148: update d->m_file in ReadOnlyPart::setUrl()

[Nathaniel Graham]

ngraham added reviewers: Frameworks, dfaure.

REPOSITORY
  R306 KParts

REVISION DETAIL
  https://phabricator.kde.org/D27148

To: pdabrowski, elvisangelaccio, ngraham, #frameworks, dfaure
Cc: marten, kde-frameworks-devel, LeGast00n, GB_2, michaelh, ngraham, bruns