Answering a query may be delayed to the moment in which we've not any
more messages in the queue, however this case can also happen just after
we've cleared the UserVerifier and in such case we'd have nothing to
answer, but we currently throw an error:
JS ERROR: Exception in callback for signal: no-more-messages:
TypeError: this._userVerifier is null
answerQuery/signalId<@resource:///org/gnome/shell/gdm/util.js:249:17
_emit@resource:///org/gnome/gjs/modules/core/_signals.js:133:47
finishMessageQueue@resource:///org/gnome/shell/gdm/util.js:266:14
_clearMessageQueue@resource:///org/gnome/shell/gdm/util.js:301:14
clear@resource:///org/gnome/shell/gdm/util.js:223:14
cancel@resource:///org/gnome/shell/gdm/util.js:205:18
reset@resource:///org/gnome/shell/gdm/authPrompt.js:482:32
cancel@resource:///org/gnome/shell/gdm/authPrompt.js:569:14
vfunc_key_press_event@resource:///org/gnome/shell/gdm/authPrompt.js:128
So handle this case more gracefully keeping track of the current
cancellable and checking whether it is still valid before trying to answer
a query or do a delayed action.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1622>
c936ca3ea0