Merge pull request #57451 from joscollin/wip-65990-reef

reef: cephfs_mirror: fix crash in update_fs_mirrors()

diff --cc src/tools/cephfs_mirror/FSMirror.h
index aaba1cb9f3a757edda950a7db43517b76958d3c0,efc743a1414c97443a40d489636308f656e6c477..b106fdff8b60d4e61b9ca47e993c189e67b2c8a3
--- 1/src/tools/cephfs_mirror/FSMirror.h
--- 2/src/tools/cephfs_mirror/FSMirror.h
+++ b/src/tools/cephfs_mirror/FSMirror.h
@@@ -47,12 -47,17 +47,17 @@@ public
  
    bool is_failed() {
      std::scoped_lock locker(m_lock);
-     return m_init_failed ||
-            m_instance_watcher->is_failed() ||
-            m_mirror_watcher->is_failed();
+     bool failed = m_init_failed;
+     if (m_instance_watcher) {
+       failed |= m_instance_watcher->is_failed();
+     }
+     if (m_mirror_watcher) {
+       failed |= m_mirror_watcher->is_failed();
+     }
+     return failed;
    }
  
 -  utime_t get_failed_ts() {
 +  monotime get_failed_ts() {
      std::scoped_lock locker(m_lock);
      if (m_instance_watcher) {
        return m_instance_watcher->get_failed_ts();