[wanproxy/wanproxy] 10d98c: Fix a livelock in CallbackThread.

[Juli Mallett]

  Branch: refs/heads/master
  Home:   https://github.com/wanproxy/wanproxy
  Commit: 10d98cbebc3d1c3b979b64accdce0914b4a38522
      https://github.com/wanproxy/wanproxy/commit/10d98cbebc3d1c3b979b64accdce0914b4a38522
  Author: Juli Mallett <juli at clockworksquid.com>
  Date:   2025-02-13 (Sat, 13 Feb 2025)
  Changed paths:
    M event/callback_thread.cc
  Log Message:
  -----------
  Fix a livelock in CallbackThread.
This can happen when all of the callbacks which are scheduled have
locks which are held by running threads which are, themselves,
blocked on the CallbackThread lock.