fix(user_ldap): Improve case where selected config is undefined

[artonge]

Multiple fixes to improve deleting a config and configuring a new one:

• Improve case where selected config is undefined
• Disable some buttons when clicking them would lead to an issue
• Properly update local variable for username and password in server settings
• Properly use fall back message in case of empty response
• Properly handle new config creation in settings

Fix #56070

[artonge]

EDIT: Found the issue, fixed in faaf850

@come-nc one weird irritating thing: when I create a new config, it is disabled by default, which is not bad. But when I test the config, while still disabled, the binding fails here:

server/apps/user_ldap/lib/Controller/ConfigAPIController.php

Lines 266 to 271 in ccabed8

	if (!$connection->bind()) {
	return new DataResponse([
	'success' => false,
	'message' => $this->l->t('Valid configuration, but binding failed. Please check the server settings and credentials.'),
	]);
	}

However, if I activate the config, it works. If I disable the config again, it works too. I tried debugging, but couldn't find any differences in the tested config before or after activating it.

Any idea?

[susnux]

otherwise it looks good