Fixing segfault with reading from BuiltinTopicDcpsTopic

[willstott101]

Mainly opening the MR to check if it reproduces on the CI - I consistently get segfault when using this builtin topic - which I wanted to use for type introspection of known topic names.

[willstott101]

The dds_builtintopic_endpoint array rcontainer in ddspy_read_endpoint in pysertype.c appears to have invalid entries. Valgrind is reporting invalid reads when rcontainer[i]->qos is accessed... even when checking if the qos is NULL.

I'm a little confused here, and would need to learn a lot to dig further. So I'm going to leave this and avoid the introspection for a while, hopefully will find a chance to come back to this.

[willstott101]

Ahah! In the cyclonedds C tests the Topic endpoint is of type dds_builtintopic_topic_t not dds_builtintopic_endpoint_t: https://github.com/eclipse-cyclonedds/cyclonedds/blob/master/src/core/ddsc/tests/topic_discovery.c#L139

So I think we need ANOTHER read/take pair for the topics in pysertype.c

[thijsmie]

Thanks for your work on this @willstott101! 🥳