Fix #1617 Sanitize input from MyBB server

Fix #1617 Sanitize input from MyBB server
I complain because it's sanitized twice now. Whatever you'll set as your useragent: urlencode will sanitize it in a way which prevents it from breaking the src tag (otherwise it wouldn't be a valid url). Also `htmlspecialchars_uni` will change "&" to "&amp;", but as we're already using "&amp;" to build the url it'll result in "&amp;amp;" which will likely stop the stas from working.