Fix no specified namespace

[ivanpauno]

If the user doesn't explicitly pass a namespace to Node action neither uses PushRosNamespace, the node namespace can't be known at launch time neither the fully qualified node name:

launch_ros/launch_ros/launch_ros/actions/node.py

Lines 355 to 358 in 7974bd4

	if self.__expanded_node_namespace != '':
	cmd_extension = ['-r', LocalSubstitution("ros_specific_arguments['ns']")]
	self.cmd.extend([normalize_to_list_of_substitutions(x) for x in cmd_extension])
	validate_namespace(self.__expanded_node_namespace)

This PR fixes that incorrect assumption.

[ivanpauno]

• Linux
• Linux-aarch64
• macOS
• Windows

[ivanpauno]

I'm not sure of how this can be backported.
It should be somehow combined with #157.

I will try to figure out if there's a no API breaking way of backporting the fix.

[jacobperron]

@ivanpauno Friendly ping. Let me know if you still plan to look at backporting this change and #157. I think backporting those changes will make other backports easier to do (currently I get conflicts since they touch similar lines of code).

[ivanpauno]

@ivanpauno Friendly ping. Let me know if you still plan to look at backporting this change and #157. I think backporting those changes will make other backports easier to do (currently I get conflicts since they touch similar lines of code).

It's hard to come up with a backport of this.
This is fixing a bug, but it's also slightly changing behavior in ways that can break existing use cases.

I would prefer not backporting this, except we get an explicit request on doing so.
In that case, I will try to come up with something.