mail-auth: We want check_cancellable, not handle_cancellation
mail-auth: We want check_cancellable, not handle_cancellation

This is a school boy mistake. We want to use
g_simple_async_result_set_check_cancellable to check the state of the
GCancellable before dispatching results, not the unrelated
g_simple_async_result_set_handle_cancellation.

https://bugzilla.gnome.org/show_bug.cgi?id=758361

ritzk/gnome-online-accounts,ritzk/gnome-online-accounts,ritzk/gnome-online-accounts