Fixed so that empty QDateTime is returned for non existing file.
Fixed also created() and lastRead() to return empty QDateTime for
non existing file.
QFileSystemEngine::fillMetaData() returned true for non existing
files. This was also corrected.
Task-number: QTBUG-25811
Change-Id: I523eb99e4405b4b813b2950f85cc646239181d07
Reviewed-by: Qt Doc Bot <qt_docbot@qt-project.org>
Reviewed-by: Christian Stromme <christian.stromme@nokia.com>