Fix garbled text in Wiki (#177)

GitHub fixes GH-176

The default value for encoding in `Nokogiri::HTML::SAX::Parser.new` has
changed since Nokogiri 1.17.0.

* 1.16.8:
https://github.com/sparklemotion/nokogiri/blob/v1.16.8/lib/nokogiri/xml/sax/parser.rb#L72
* `def initialize(doc = Nokogiri::XML::SAX::Document.new, encoding =
"UTF-8")`
* 1.17.0:
https://github.com/sparklemotion/nokogiri/blob/v1.17.0/lib/nokogiri/xml/sax/parser.rb#L95
* `def initialize(doc = Nokogiri::XML::SAX::Document.new, encoding =
nil)`
*
sparklemotion/nokogiri@35596e7#diff-116e772eb2e47bb59e0798183732d07ef3312e480c764a6dc34b09f743a73f8c

This causes the encoding to be unspecified, resulting in garbled text.
Therefore, we changed it to specify `html.encoding`.

---------

Co-authored-by: Sutou Kouhei <kou@cozmixng.org>

Author: abetomo

lib/full_text_search/markup_parser.rb

@@ -18,7 +18,9 @@ def parse(object, attribute, options={})
       return ["", []] unless html.present?
 
       document = Document.new
-      parser = Nokogiri::HTML::SAX::Parser.new(document)
+      # We need .to_s for old Nokogiri. We can remove the .to_s after we drop support for Redmine < 6.0.
+      # Redmine 6.0 requires Nokogiri 1.18.3 or later.
+      parser = Nokogiri::HTML::SAX::Parser.new(document, html.encoding.to_s)
       parser.parse(html)
       [document.text.strip, document.tag_ids]
     end