Handle nullptr callbacks correctly in WaitSet and Listener

[dkroenke]

Brief description

When checking the WaitSet and Listener tests with ASAN on gcc an error is thrown that a nullptr is de-referenced when a nullptr is passed as callback function to functions like iox_ws_attach_subscriber_event or iox_listener_attach_subscriber_event in the C-Binding.

In the WaitSet it should be possible for the users to use nullptr callback arguments if they want to wait in a loop.

Reference Links:
#918 (comment)
#918 (comment)

• Enable in CI the ASAN check with latest gcc compiler
• Refactor WaitSet and Listener to accept (or disallow) nullptr arguments
• Test explicitly against this

[elBoberido]

@dkroenke I noticed that the tasks are not checked. Are they all done or this this issue need to be reopened?

[dkroenke]

@elBoberido All done