Ensure eeconfig initialised before reading EEPROM handedness.

[daskygit]

Description

I noticed while using transient EEPROM and EE_HANDS that flashing using uf2-split-left, the left side matrix behaved as the right but the LEDs behaved correctly. This appears to be due to the eeconfig handedness being read before it's initialised returning 0.

I've added a check to split_pre_init to ensure eeconfig is enabled and initialise if not.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).