Create a no operation credential provider and fix a number of other issues
Review Request #456 — Created Jan. 26, 2021 and submitted — Latest diff uploaded
* Create a "None" credential provider that allows users to disable credential storing and only allows them to enter passwords manually. * Use g_signal_connect_object in PidginCredentialProviderStore. * Move purple_credential_manager_shutdown after purple_plugins_uninit. * Set the active credential provider to NULL during shutdown.
Compiled and ran locally verified that we no long hang on exit if we've opened the preferences window.