Fix weird behavior when opening a QFileDialog for non-current directory.
Fix weird behavior when opening a QFileDialog for non-current directory.

shouldShowFileName() can be called with an empty filename, but must not
create and use a QFileInfo("") since that has known undefined behavior.
So just return NO right away for empty filenames.

Merge-request: 1765
Reviewed-by: Richard Moe Gustavsen <881e230b58d8abf8efbd9b8ce5a2db05f1d53614@nokia.com>

radekp/qt,radekp/qt,pruiz/wkhtmltopdf-qt,radekp/qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,radekp/qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,igor-sfdc/qt-wk,igor-sfdc/qt-wk,radekp/qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,radekp/qt,radekp/qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,radekp/qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,radekp/qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,radekp/qt