Qt: preferences, fix conflict detection.

Should close #3823 and #5052

modules/gui/qt4/components/preferences_widgets.cpp

@@ -1550,8 +1550,8 @@ void KeyInputDialog::checkForConflicts( int i_vlckey )
                           b_global ? 2 : 1 );
 
     if( conflictList.count() &&
-        conflictList[0]->data( b_global ? 2 : 1, Qt::UserRole ).toInt() > 1 )
-        /* Avoid 0 or -1 that are the "Unset" states */
+        !conflictList[0]->data( b_global ? 2 : 1, Qt::UserRole ).toString().isEmpty() &&
+         conflictList[0]->data( b_global ? 2 : 1, Qt::UserRole ).toString() != "Unset" )
     {
         warning->setText( qtr("Warning: the key is already assigned to \"") +
                 conflictList[0]->text( 0 ) + "\"" );