Fix title sort bug, invalidate titles of the Library

Refactor remove cache

src/util/util.cr

@@ -91,25 +91,25 @@ def sort_titles(titles : Array(Title), opt : SortOptions, username : String)
   cached_titles = LRUCache.get cache_key
   return cached_titles if cached_titles.is_a? Array(Title)
 
-  ary = titles
-
   case opt.method
   when .time_modified?
-    ary.sort { |a, b| (a.mtime <=> b.mtime).or \
+    ary = titles.sort { |a, b| (a.mtime <=> b.mtime).or \
       compare_numerically a.sort_title, b.sort_title }
   when .progress?
-    ary.sort do |a, b|
+    ary = titles.sort do |a, b|
       (a.load_percentage(username) <=> b.load_percentage(username)).or \
         compare_numerically a.sort_title, b.sort_title
     end
   when .title?
-    ary.sort { |a, b| compare_numerically a.sort_title, b.sort_title }
+    ary = titles.sort do |a, b|
+      compare_numerically a.sort_title, b.sort_title
+    end
   else
     unless opt.method.auto?
       Logger.warn "Unknown sorting method #{opt.not_nil!.method}. Using " \
                   "Auto instead"
     end
-    ary.sort { |a, b| compare_numerically a.sort_title, b.sort_title }
+    ary = titles.sort { |a, b| compare_numerically a.sort_title, b.sort_title }
   end
 
   ary.reverse! unless opt.not_nil!.ascend
@@ -118,6 +118,18 @@ def sort_titles(titles : Array(Title), opt : SortOptions, username : String)
   ary
 end
 
+def remove_sorted_titles_cache(titles : Array(Title),
+                               sort_methods : Array(SortMethod),
+                               username : String)
+  [false, true].each do |ascend|
+    sort_methods.each do |sort_method|
+      sorted_titles_cache_key = SortedTitlesCacheEntry.gen_key username,
+        titles, SortOptions.new(sort_method, ascend)
+      LRUCache.invalidate sorted_titles_cache_key
+    end
+  end
+end
+
 class String
   # Returns the similarity (in [0, 1]) of two paths.
   # For the two paths, separate them into arrays of components, count the