timidity: fix playing over JACK with -iA -Oj

Based on https://bugs.archlinux.org/task/40906#comment124519

pkgs/tools/misc/timidity/default.nix

@@ -8,6 +8,8 @@ stdenv.mkDerivation {
     sha256 = "1xf8n6dqzvi6nr2asags12ijbj1lwk1hgl3s27vm2szib8ww07qn";
   };
 
+  patches = [ ./timidity-iA-Oj.patch ];
+
   nativeBuildInputs = [ pkgconfig ];
   buildInputs = [ alsaLib libjack2 ncurses ];
 

pkgs/tools/misc/timidity/timidity-iA-Oj.patch

@@ -0,0 +1,14 @@
+Without this timidity -iA -Oj prints "Couldn't start JACK device (`j')"
+and does not play MIDI.
+
+--- a/timidity/jack_a.c
++++ b/timidity/jack_a.c
+@@ -513,6 +513,8 @@ static int actl_jack(int request, void *arg)
+ 		ringbuf_clear(&ctx->rbuf);
+ 		return 0;
+ 
++	case PM_REQ_PLAY_START:
++		return 0;
+ 	}
+ 	return -1;
+ }