Go: fixing racing condition on app start.

Request procesing loop should be started in ready handler to avoid race
between go-routine start and context ready flag assignment.

The issue introduced in 43553aa72111.

go/nxt_cgo_lib.c

@@ -30,6 +30,7 @@ nxt_cgo_run(uintptr_t handler)
     init.callbacks.port_send       = nxt_cgo_port_send;
     init.callbacks.port_recv       = nxt_cgo_port_recv;
     init.callbacks.shm_ack_handler = nxt_go_shm_ack_handler;
+    init.callbacks.ready_handler   = nxt_go_ready;
 
     init.data = (void *) handler;
 

go/port.go

@@ -110,11 +110,14 @@ func nxt_go_add_port(ctx *C.nxt_unit_ctx_t, p *C.nxt_unit_port_t) C.int {
 	p.in_fd = -1
 	p.out_fd = -1
 
-	if new_port.key.id == 65535 {
+	return C.NXT_UNIT_OK
+}
+
+//export nxt_go_ready
+func nxt_go_ready(ctx *C.nxt_unit_ctx_t) C.int {
 	go func(ctx *C.nxt_unit_ctx_t) {
-			C.nxt_unit_run_shared(ctx);
+		C.nxt_unit_run_shared(ctx)
 	}(ctx)
-	}
 
 	return C.NXT_UNIT_OK
 }