When setting the mime filter, check that the QMimeType we get from
QMimeDatabase::mimeTypeForName() is valid before adding it to the mime
filter list. This fixes a bug where if the QMimeType is invalid its name
(and comment) property is empty, leading to empty entries in the filter
widget drop-down menu.
Per dfaure's recommendation, display a warning about the invalid mimeType.
Also install the necessary Qt logging catergory bits for KFileWidgets.
BUG: 417355
FIXED-IN: 5.68