Fixing Go program crash.

Go request registration should be removed before C request memory freed.

C request address used as a key in Go map.  Freed memory can be instantly
reused for other request and older request registration should removed at this
point to avoid collisions.

src/go/unit/request.go

@@ -107,10 +107,10 @@ func (r *request) response() *response {
 }
 
 func (r *request) done() {
-	C.nxt_go_request_done(r.c_req)
-
 	remove_request(r)
 
+	C.nxt_go_request_done(r.c_req)
+
 	for _, m := range r.msgs {
 		m.Close()
 	}