Fix negative exponent for sub Hz frequency value

[nitin-io]

Summary

When the refresh rate drops below 1 Hz, the exponent calculation can produce -1:

Math.floor(Math.log(value) / Math.log(unit))

Since the frequency unit array starts at Hz and does not contain negative indices, this results in an undefined unit lookup.

This change clamps the exponent to a minimum value of 0:

Math.max(0, Math.floor(Math.log(value) / Math.log(unit)))

This prevents invalid array access while preserving existing behavior for Hz, KHz, MHz, and GHz values.

Testing

• Verified normal frequency formatting.
• Verified GHz values are unaffected.
• Verified values below 1 Hz no longer produce undefined units.

Fix for Issue: #555