Fix check if theming defaults instance is available
Fix check if theming defaults instance is available

The check in URLGenerator.php#169 and Server.php#945 are different and thus the DI container could return a \OC_Defaults object which does not provide the wanted method caising a PHP error.

Fixes #8420

Signed-off-by: Morris Jobke <7f550a9f4c44173a37664d938f1355f0f92a47a7@morrisjobke.de>

andreas-p/nextcloud-server,nextcloud/server,nextcloud/server,andreas-p/nextcloud-server,andreas-p/nextcloud-server,nextcloud/server,nextcloud/server,andreas-p/nextcloud-server,andreas-p/nextcloud-server