Fix bug not setting general rules after media query

This commit fixes a bug in CssParser::Parser#parse_block_into_rule_sets!
where the media_type was not being set for general rules that followed a
media query rule. This bug subsequently led to the result of
CssParser::Parser#to_s producing css strings that lacked these specific
rules, since that method organizes styles by media type.

The fix was to set the `current_media_queries` variable inside
`#parse_block_into_rule_sets!` back to `:all` after we finish iterating
through a media query, since that is the default state.