When iterating over diagnostics channel subscribers, assume their count
is zero if the list of subscribers becomes undefined, because there may
be only one subscriber which may unsubscribe itself as part of its
onMessage handler.
Signed-off-by: Gabriel Schulhof <gabrielschulhof@gmail.com>
PR-URL: https://github.com/nodejs/node/pull/48933
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: theanarkh <theratliter@gmail.com>
