[dacp] Increase current revision number even if there are no open req…

…uests

This change aligns with iTunes behavior. It also means that a client that is
not long polling can use the revision number (cmsr) value to check for changes.

src/httpd_dacp.c

@@ -698,14 +698,14 @@ playstatusupdate_cb(int fd, short what, void *arg)
   read(update_pipe[0], &dummy, sizeof(dummy));
 #endif
 
+  current_rev++;
+
   if (!update_requests)
     goto readd;
 
   CHECK_NULL(L_DACP, evbuf = evbuffer_new());
   CHECK_NULL(L_DACP, update = evbuffer_new());
 
-  current_rev++;
-
   ret = make_playstatusupdate(update);
   if (ret < 0)
     goto out_free_update;