[MeL] Fix getOrCreateMeshProperty for IP data.

For an existing, non-empty mesh property on integration
points the check fails and it is not possible to know
what the size of this data should be.
Omitting the assertion for this case.

MeshLib/Mesh.h

@@ -268,7 +268,13 @@ PropertyVector<T>* getOrCreateMeshProperty(Mesh& mesh,
         auto result =
             mesh.getProperties().template getPropertyVector<T>(property_name);
         assert(result);
-        assert(result->size() == numberOfMeshItems() * number_of_components);
+        if (item_type != MeshItemType::IntegrationPoint)
+        {
+            // Test the size if number of mesh items is known, which is not the
+            // case for the integration point data.
+            assert(result->size() ==
+                   numberOfMeshItems() * number_of_components);
+        }
         return result;
     }