Fix slash command children in groups matching children with the same name

Pull Request

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Pull Request Information

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• [X] My PR fixes a bug, error, or other issue with the library's codebase.
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Description

Currently, when checking if a slash command children matches the interaction, the client does not properly check if the child is in not in a group. This PR fixes that by making sure that a command with a child only matches children without a subcommand, and that slash commands with children and a group match the same group, and do not throw NPEs while checking.

Will do some testing on this in a bit.