fix error on downgrade for SEB Settings

src/main/java/ch/ethz/seb/sebserver/gui/service/examconfig/impl/AttributeMapping.java

@@ -72,6 +72,7 @@ public class AttributeMapping {
 
         this.orientationAttributeNameMapping = Utils.immutableMapOf(orientations
                 .stream()
+                .filter(o -> this.attributeIdMapping.containsKey(o.attributeId))
                 .collect(Collectors.toMap(
                         o -> this.attributeIdMapping.get(o.attributeId).name,
                         Function.identity())));