Add a proper error message when trying to add node to a group with an empty name

[suhankins]

Right now, if you try to add a node to a group with an empty name, you will get a very unhelpful error
Condition "!p_identifier.operator String().length()" is true.

This pull request adds an error message "Tried to add node to a group with an empty name."

Minimal reproduction build:
error-message-test.zip

[AdrienUfferte]

Simple and effective. This is my first review, do not take it into account like an experimented one!

[Ivorforce]

Good idea!
Wording sounds good to me.

[akien-mga]

Looks good! Could you squash the commits? See PR workflow for instructions.

[suhankins]

Looks good! Could you squash the commits? See PR workflow for instructions.

Hopefully I did it correctly.

[akien-mga]

Mostly good, but you kept the message of the last commit instead of the first one, so it's not fully accurate.
It would be better to change it to "Add a proper error message when trying to add node to a group with an empty name" like the PR's title (and no need to mention reviewers or add as co-authors for such small edits :)).

You can change the commit message with git commit --amend and the git push --force.

[suhankins]

Mostly good, but you kept the message of the last commit instead of the first one, so it's not fully accurate. It would be better to change it to "Add a proper error message when trying to add node to a group with an empty name" like the PR's title (and no need to mention reviewers or add as co-authors for such small edits :)).

You can change the commit message with git commit --amend and the git push --force.

Okay, thank you. Should be good now.

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉