fix(split): Properly return from command handler

[ReFil]

#3103 introduced a small bug where spurious HID indicator events with garbage data would be raised on the peripheral when behaviours are invoked as the switch statement didn't return in each case and continued to chain down. This properly returns from each case to stop this happening

PR check-list

• Branch has a clean commit history
• Additional tests are included, if changing behaviors/core code that is testable.
• Proper Copyright + License headers added to applicable files (Generally, we stick to "The ZMK Contributors" for copyrights to help avoid churn when files get edited)
• Pre-commit used to check formatting of files, commit messages, etc.
• Includes any necessary documentation changes.