favoritescontroller#destroy should work even if the post doesn't exist, remove from favorites on expunge (fixes #3222)

app/controllers/favorites_controller.rb

@@ -47,12 +47,19 @@ class FavoritesController < ApplicationController
   end
 
   def destroy
-    @post = Post.find(params[:id])
-    @post.remove_favorite!(CurrentUser.user)
+    @post = Post.find_by_id(params[:id])
+
+    if @post
+      @post.remove_favorite!(CurrentUser.user)
+      path = mobile_post_path(@post)
+    else
+      Favorite.remove(post_id: params[:id], user: CurrentUser.user)
+      path = mobile_posts_path
+    end
 
     respond_with(@post) do |format|
       format.html do
-        redirect_to(mobile_post_path(@post))
+        redirect_to(path)
       end
       format.js
       format.json do