[Misc] Fix all remaining (hopefully) issues with frozen string literals

+"" is a bit of a copout, that could be done better but very easy to do in these more complicated cases

app/helpers/comments_helper.rb

@@ -4,7 +4,7 @@ module CommentsHelper
 
     voted = !vote.nil?
     vote_score = voted ? vote.score : 0
-    comment_score = comment.score
+    score_tag = tag.li(comment.score, class: "comment-score #{score_class(comment.score)}", id: "comment-score-#{comment.id}")
 
     if CurrentUser.is_member?
       up_tag = tag.li(
@@ -17,10 +17,9 @@ module CommentsHelper
         class: confirm_score_class(vote_score, -1, false),
         id: "comment-vote-down-#{comment.id}",
       )
-    else
-      up_tag = down_tag = "".html_safe
-    end
-    score_tag = tag.li(comment.score, class: "comment-score #{score_class(comment_score)}", id: "comment-score-#{comment.id}")
       up_tag + score_tag + down_tag
+    else
+      score_tag
+    end
   end
 end

app/helpers/note_versions_helper.rb

@@ -1,30 +1,22 @@
 module NoteVersionsHelper
   def note_version_body_diff_info(note_version)
     previous = note_version.previous
-    if previous.nil?
-      return ""
+    if note_version.body == previous&.body
+      tag.span("(body not changed)", class: "inactive")
+    else
+      ""
     end
-
-    html = ""
-    if note_version.body == previous.body
-      html += '<span class="inactive">(body not changed)</span>'
-    end
-
-    html.html_safe
   end
 
   def note_version_position_diff(note_version)
     previous = note_version.previous
+    html = "#{note_version.width}x#{note_version.height} #{note_version.x},#{note_version.y}"
+    return html if previous.nil?
 
-    html = "#{note_version.width}x#{note_version.height}"
-    html += " #{note_version.x},#{note_version.y}"
-    if previous.nil?
-      html
-    elsif note_version.x == previous.x && note_version.y == previous.y && note_version.width == previous.width && note_version.height == previous.height
+    if note_version.x == previous.x && note_version.y == previous.y && note_version.width == previous.width && note_version.height == previous.height
       html
     else
-      html = '<span style="text-decoration: underline;">' + html + '</span>'
-      html.html_safe
+      tag.span(html, style: "text-decoration: underline;")
     end
   end
 end

app/helpers/posts_helper.rb

@@ -35,7 +35,7 @@ module PostsHelper
   end
 
   def has_parent_message(post, parent_post_set)
-    html = ""
+    html = +""
 
     html << "Parent: "
     html << link_to("post ##{post.parent_id}", post_path(id: post.parent_id))
@@ -56,7 +56,7 @@ module PostsHelper
   end
 
   def has_children_message(post, children_post_set)
-    html = ""
+    html = +""
 
     html << "Children: "
     text = children_post_set.children.count == 1 ? "1 child" : "#{children_post_set.children.count} children"

app/logical/apng_inspector.rb

@@ -35,7 +35,7 @@ class ApngInspector
       #We could be dealing with large number of chunks,
       #so the code should be optimized to create as few objects as possible.
       #All literal strings are frozen and read() function uses string buffer.
-      chunkheader = ''
+      chunkheader = +""
       while file.read(8, chunkheader)
         #ensure that first 8 bytes from chunk were read properly
         if chunkheader == nil || chunkheader.length < 8

app/presenters/tag_set_presenter.rb

@@ -16,7 +16,7 @@ class TagSetPresenter < Presenter
   end
 
   def post_index_sidebar_tag_list_html(current_query: "")
-    html = ""
+    html = +""
     if ordered_tags.present?
       html << '<ul>'
       ordered_tags.each do |tag|
@@ -29,7 +29,7 @@ class TagSetPresenter < Presenter
   end
 
   def post_show_sidebar_tag_list_html(current_query: "", highlighted_tags:)
-    html = ""
+    html = +""
 
     TagCategory::SPLIT_HEADER_LIST.each do |category|
       typetags = tags_for_category(category)