FileChooser: Properly preselect MIME filter passed as "current_filter"
This fixes the preselection of a MIME type filter passed as current_filter
.
Other than the KFileWidget::setFilter
case,
calling KFileWidget::setMimeFilter
does not select the first filter
in the list, but takes an explicit (optional) parameter which of the
filters to preselect, "otherwise, a first item showing all the mimetypes
will be created". (https://api.kde.org/frameworks/kio/html/classKFileWidget.html#acdb884df2e08aa11c92adc1f96b6b2c1)
In order to test this, the sample program from QTBUG-85658 can be used (together with a Qt version that contains the fix for that one).
In step 6 of the steps to reproduce described there, "plain text document, PDF document" is preselected in the file dialog without this fix here present, whereas it should be just "plain text document".