player: fix leak on client-message send failure

when there's a flood of events causing the event queue to
overflow, the duplicated client-message payload gets dropped
without being released. free it on failure too.

discovered while trying to trigger #10110.

player/client.c

@@ -818,11 +818,13 @@ int mp_client_send_event(struct MPContext *mpctx, const char *client_name,
         r = send_event(ctx, &event_data, false);
     } else {
         r = -1;
-        talloc_free(data);
     }
 
     mp_mutex_unlock(&clients->lock);
 
+    if (r < 0)
+        talloc_free(data);
+
     return r;
 }