[http] Also allow remote playlists to have https streams (fixes #1251)

Fix it by adding net_is_http_or_https() utility function in misc.h and make
sure it used whenever a http protocol check is made.

src/misc.c

@@ -363,6 +363,11 @@ net_evhttp_bind(struct evhttp *evhttp, short unsigned port, const char *log_serv
     }
 */
 
+bool
+net_is_http_or_https(const char *url)
+{
+  return (strncasecmp(url, "http://", strlen("http://")) == 0 || strncasecmp(url, "https://", strlen("https://")) == 0);
+}
 
 /* ----------------------- Conversion/hashing/sanitizers -------------------- */