upstream: fix mutex lock on pending destroy connections

Signed-off-by: Eduardo Silva <[email protected]>

src/flb_upstream.c

@@ -842,7 +842,7 @@ int flb_upstream_conn_pending_destroy(struct flb_upstream *u)
  }
 
  if (u->thread_safe == FLB_TRUE) {
- pthread_mutex_lock(&u->mutex_lists);
+ pthread_mutex_unlock(&u->mutex_lists);
  }
 
  return 0;