lavf: add libopenmpt demuxer

Fixes ticket #5623

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/allformats.c

@@ -375,6 +375,7 @@ void av_register_all(void)
     REGISTER_DEMUXER (LIBGME,           libgme);
     REGISTER_DEMUXER (LIBMODPLUG,       libmodplug);
     REGISTER_MUXDEMUX(LIBNUT,           libnut);
+    REGISTER_DEMUXER (LIBOPENMPT,       libopenmpt);
 
     initialized = 1;
 }