Check message creation in zenoh before running local callback

[caguero]

🦟 Bug fix

Fixes this issue.

This patch avoids a crash when the CreateMessage() function wasn't able to create a message. When using zenoh, we weren't checking whether the message was successfully created or not.

Note that CreateMessage() doesn't have to always create a message, there are situations where it's not possible to do. The most common case is when the publisher publishes a custom message and the subscriber doesn't have access to that message definition. This is what happens in the reported issue, gz topic echo shouldn't work (unless it has access to the .desc message files) but in any case it should not crash.

How to test it?

Compile the examples:

cd <jetty_ws>/src/gz-transport/example
mkdir build && cd build
make -j

In terminal 1:

./publisher_custom_msg

In terminal 2:

gz topic -e -t /foo

No output should appear on the terminal but nothing should crash.

Summary

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
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• All tests passed (See test coverage)
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