Fix related tags overflow in detachable tag edit dialog (fix #3219).

Bug: resizing the tag edit dialog then expanding the related tags
section doesn't resize the dialog to fit the expanded related tags
section. Instead a scrollbar appears.

Fixes this by expanding the dialog's height when the related tags are
shown.

app/assets/javascripts/related_tag.js

@@ -287,6 +287,7 @@
   Danbooru.RelatedTag.show = function() {
     $("#related-tags").show()
     $("#toggle-related-tags-link").text("«");
+    $("#edit-dialog").height("auto");
   }
 
   Danbooru.RelatedTag.hide = function() {