Include base type in the set of dependent types

Without including the base type in the dependent types, the initial call to construct a
DDS topic succeeds at the C API level, but then constructing a C-based deserialiser for
extracting the key fields within the Python binding fails because the base type
is (potentially) still undefined in the type library in Cyclone.  This results in a "bad
parameter" exception.

Signed-off-by: Erik Boasson <eb@ilities.com>

cyclonedds/idl/_xt_builder.py

@@ -406,6 +406,20 @@ def gather_types(cls, _type):
 
                     graph[my_node_name].add(scan_node_name)
 
+            if isclass(_ctype) and issubclass(_ctype, IdlStruct):
+                # get_extended_type_hints will not inspect the base type, which is a struct
+                base_type = _ctype.__base__
+                if base_type is None or base_type == IdlStruct:
+                    pass
+                else:
+                    print("base type!")
+                    scan_node_name = base_type.__idl_typename__.replace('.', '::')
+                    if scan_node_name not in graph:
+                        graph[scan_node_name] = set()
+                        graph_types[scan_node_name] = base_type
+
+                    graph[my_node_name].add(scan_node_name)
+
             for name, fieldtype in get_extended_type_hints(_ctype).items():
                 m, deep = cls._deep_gather_type(fieldtype)
                 plain = cls._impl_xt_is_plain(fieldtype)