* lib/cgi/util.rb(CGI.escapeHTML): performance improvement.

thank you @bbxiao1 via
  https://github.com/ruby/ruby/pull/333

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41431 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/cgi/util.rb

@@ -42,7 +42,8 @@ module CGI::Util
   #      # => "Usage: foo \"bar\" <baz>"
   def unescapeHTML(string)
     enc = string.encoding
-    if [Encoding::UTF_16BE, Encoding::UTF_16LE, Encoding::UTF_32BE, Encoding::UTF_32LE].include?(enc)
+    return string unless string.include? '&'
+    if enc != Encoding::UTF_8 && [Encoding::UTF_16BE, Encoding::UTF_16LE, Encoding::UTF_32BE, Encoding::UTF_32LE].include?(enc)
       return string.gsub(Regexp.new('&(apos|amp|quot|gt|lt|#[0-9]+|#x[0-9A-Fa-f]+);'.encode(enc))) do
         case $1.encode(Encoding::US_ASCII)
         when 'apos'                then "'".encode(enc)