Fix an error when parsing attribute without quotes and value

[Earlopain]

I stumbled across the following html snippet which crashes the parser: <div foo=>bar</div>. The interpreted html from browsers (both chrome and firefox) is <div foo="">bar</div> so the generated ast with the fix seems to make sense to me.

Error trace

/home/earlopain/.rbenv/versions/3.3.4/lib/ruby/gems/3.3.0/gems/parser-3.3.4.2/lib/parser/source/range.rb:39:in `initialize': Parser::Source::Range: end_pos must not be less than begin_pos (ArgumentError)

          raise ArgumentError, 'Parser::Source::Range: end_pos must not be less than begin_pos'
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        from /home/earlopain/.rbenv/versions/3.3.4/lib/ruby/gems/3.3.0/gems/better_html-2.1.1/lib/better_html/tokenizer/location.rb:23:in `initialize'
        from /home/earlopain/.rbenv/versions/3.3.4/lib/ruby/gems/3.3.0/gems/better_html-2.1.1/lib/better_html/parser.rb:214:in `new'
        from /home/earlopain/.rbenv/versions/3.3.4/lib/ruby/gems/3.3.0/gems/better_html-2.1.1/lib/better_html/parser.rb:214:in `build_location'
        from /home/earlopain/.rbenv/versions/3.3.4/lib/ruby/gems/3.3.0/gems/better_html-2.1.1/lib/better_html/parser.rb:206:in `build_node'
        from /home/earlopain/.rbenv/versions/3.3.4/lib/ruby/gems/3.3.0/gems/better_html-2.1.1/lib/better_html/parser.rb:177:in `build_attribute_node'
        from /home/earlopain/.rbenv/versions/3.3.4/lib/ruby/gems/3.3.0/gems/better_html-2.1.1/lib/better_html/parser.rb:151:in `build_tag_attributes_node'
        from /home/earlopain/.rbenv/versions/3.3.4/lib/ruby/gems/3.3.0/gems/better_html-2.1.1/lib/better_html/parser.rb:133:in `build_tag_node'
        from /home/earlopain/.rbenv/versions/3.3.4/lib/ruby/gems/3.3.0/gems/better_html-2.1.1/lib/better_html/parser.rb:79:in `build_document_node'
        from /home/earlopain/.rbenv/versions/3.3.4/lib/ruby/gems/3.3.0/gems/better_html-2.1.1/lib/better_html/parser.rb:49:in `ast'