Fix empty password for provisioned account

Passwords can't just be `null` but also an empty string. The code did
not handle that properly. Now checking against `emtpy` so both `null`
and `''` trigger shortcut evaluation and prevent decrypring of an
invalid value.

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

lib/Service/Provisioning/Manager.php

@@ -162,9 +162,9 @@ class Manager {
 		try {
 			$account = $this->mailAccountMapper->findProvisionedAccount($user);
 
-			if ($account->getInboundPassword() !== null
+			if (!empty($account->getInboundPassword())
 				&& $this->crypto->decrypt($account->getInboundPassword()) === $password
-				&& $account->getOutboundPassword() !== null
+				&& !empty($account->getOutboundPassword())
 				&& $this->crypto->decrypt($account->getOutboundPassword()) === $password) {
 				$this->logger->debug('Password of provisioned account is up to date');
 				return;