warn: fix display of specialized input prompts

Closes wikimedia-gadgets#659.  Changing changing a selection via `jquery.chosen` didn't trigger `change_subcategory`.  We still need the extra `Twinkle.warn.callback.change_subcategory(e)` call from wikimedia-gadgets#432 to update display on simply `change_category` but I don't think we need the initial event in `sub_group` if we're using chosen

modules/twinklewarn.js

@@ -98,7 +98,7 @@ Twinkle.warn.callback = function twinklewarnCallback() {
 		main_group.append( { type: 'option', label: 'Custom warnings', value: 'custom', selected: ( defaultGroup === 9 ) } );
 	}
 
-	main_select.append( { type: 'select', name: 'sub_group', event:Twinkle.warn.callback.change_subcategory } ); //Will be empty to begin with.
+	main_select.append( { type: 'select', name: 'sub_group'} ); // Event to be added alongside jquery.chosen later
 
 	form.append( {
 			type: 'input',
@@ -1149,18 +1149,20 @@ Twinkle.warn.callback.change_category = function twinklewarnCallbackChangeCatego
 		} );
 	}
 
-	$('select[name=sub_group]').chosen({width: '100%', search_contains: true});
-
-	// Limit the max height of select dropdown to prevent dialog box from becoming scrollable
-	$('.chosen-results').css({'overflow': 'auto', 'max-height': '180px'});
-
 	// clear overridden label on article textbox
 	Morebits.quickForm.setElementTooltipVisibility(e.target.root.article, true);
 	Morebits.quickForm.resetElementLabel(e.target.root.article);
 	// hide the big red notice
 	$("#tw-warn-red-notice").remove();
-	// add custom label.redWarning
+	// Trigger custom label/change on main category change
 	Twinkle.warn.callback.change_subcategory(e);
+
+	// Build select menu with jquery.chosen
+	$('select[name=sub_group]').chosen({width: '100%', search_contains: true}).change(function(e) {
+		Twinkle.warn.callback.change_subcategory(e);
+	});
+	// Limit the max height of select dropdown to prevent dialog box from becoming scrollable
+	$('.chosen-results').css({'overflow': 'auto', 'max-height': '180px'});
 };
 
 Twinkle.warn.callback.change_subcategory = function twinklewarnCallbackChangeSubcategory(e) {