PLS: replace HTTP in Ref1 with MMSH rather than MMS (fixes #4494)

If the playlist file says HTTP, we really should not try MMS over TCP
or MMS over UDP, but only MMS over HTTP.
(cherry picked from commit f0c3d6fb0b9c33b06753cf60c724ee1c3fd2dd40)

modules/demux/playlist/pls.c

@@ -169,12 +169,7 @@ static int Demux( demux_t *p_demux )
             if( !strncasecmp( psz_key, "Ref", sizeof("Ref") -1 ) )
             {
                 if( !strncasecmp( psz_mrl, "http://", sizeof("http://") -1 ) )
-                {
-                    psz_mrl++;
-                    psz_mrl[0] = 'm';
-                    psz_mrl[1] = 'm';
-                    psz_mrl[2] = 's';
-                }
+                    memcpy( psz_mrl, "mmsh", 4 );
             }
         }
         else if( !strncasecmp( psz_key, "title", sizeof("title") -1 ) )