[480] Fix inheritance support in DomainConverter

The previous condition did not account for the sentinel element.

Bug: #480
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>

backend/sirius-web-emf/src/main/java/org/eclipse/sirius/web/emf/domain/DomainConverter.java

@@ -75,7 +75,7 @@ public Optional<EPackage> convert(Domain domain) {
                 leftToConvert.addLast(candidate);
             }
         }
-        if (leftToConvert.isEmpty()) {
+        if (leftToConvert.size() == 1) {
             for (Entity entity : domain.getTypes()) {
                 EClass eClass = convertedTypes.get(entity);
                 for (Relation relation : entity.getRelations()) {