fix check and improve error message

Signed-off-by: Bjoern Schiessle <bjoern@schiessle.org>

core/Command/Encryption/ChangeKeyStorageRoot.php

@@ -146,8 +146,8 @@ class ChangeKeyStorageRoot extends Command {
 			'ownCloud will detect this folder as key storage root only if this file exists'
 		);
 
-		if ($result !== true) {
-			throw new \Exception("Can't write to new root folder. Please check the permissions and try again");
+		if (!$result) {
+			throw new \Exception("Can't access the new root folder. Please check the permissions and make sure that the folder is in your data folder");
 		}
 
 	}