OO-4190: Use the last modify of the file to create the document key (patch S. Clemenz)

src/main/java/org/olat/core/commons/services/doceditor/onlyoffice/manager/OnlyOfficeServiceImpl.java

@@ -206,7 +206,7 @@ public class OnlyOfficeServiceImpl implements OnlyOfficeService {
 	}
 
 	private String getDocumentKey(VFSMetadata metadata) {
-		String lastModified = LAST_MODIFIED.format(metadata.getLastModified());
+		String lastModified = LAST_MODIFIED.format(metadata.getFileLastModified());
 		return metadata.getUuid() + "-" + lastModified;
 	}