Fix #5132: Modqueue displays active posts when excluding any search term

Fix a bug where searching for a negated tag inside the modqueue would show
active posts.

The bug was that in a search like this:

    Post.in_modqueue.user_tag_match("-solo")

The `in_modqueue` condition would get sucked inside the tag search and negated
when we tried to apply the negation operator to the "solo" tag. So effectively
the `in_modqueue` condition would get negated and we would end up searching for
everything not in the modqueue.

app/models/post.rb

@@ -1390,7 +1390,8 @@ class Post < ApplicationRecord
       def user_tag_match(query, user = CurrentUser.user, tag_limit: user.tag_query_limit, safe_mode: CurrentUser.safe_mode?)
         post_query = PostQuery.normalize(query, current_user: user, tag_limit: tag_limit, safe_mode: safe_mode)
         post_query.validate_tag_limit!
-        post_query.with_implicit_metatags.posts
+        posts = post_query.with_implicit_metatags.posts
+        merge(posts)
       end
 
       def search(params, current_user)
@@ -1408,7 +1409,7 @@ class Post < ApplicationRecord
         )
 
         if params[:tags].present?
-          q = q.user_tag_match(params[:tags])
+          q = q.user_tag_match(params[:tags], current_user)
         end
 
         if params[:order].present?