[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.h

@@ -54,6 +54,9 @@ net_bind(short unsigned *port, int type, const char *log_service_name);
 int
 net_evhttp_bind(struct evhttp *evhttp, short unsigned port, const char *log_service_name);
 
+// Just checks if the protocol is http or https
+bool
+net_is_http_or_https(const char *url);
 
 /* ----------------------- Conversion/hashing/sanitizers -------------------- */