fix(ocm-sharing): The owner needs to be set for sharing to work

The specification says that the display name is optional and can thus
be empty, and in fact it is from oCIS and CERNBox shares.

The correct thing to set is the required opaque id from the remote
provider, the `owner` which will allways be there.

Signed-off-by: Micke Nordin <kano@sunet.se>

apps/federatedfilesharing/lib/OCM/CloudFederationProviderFiles.php

@@ -108,7 +108,7 @@ class CloudFederationProviderFiles implements ISignedCloudFederationProvider {
 
 		$token = $share->getShareSecret();
 		$name = $share->getResourceName();
-		$owner = $share->getOwnerDisplayName();
+		$owner = $share->getOwnerDisplayName() ?: $share->getOwner();
 		$sharedBy = $share->getSharedByDisplayName();
 		$shareWith = $share->getShareWith();
 		$remoteId = $share->getProviderId();