Chart series colours stop at seriesColor5

Only seriesColor1 through seriesColor5 exist. A chart with a sixth series falls back to a built-in colour that is not in the configured palette.

Steps to reproduce
1. Build a donut or series chart with six segments
2. Set seriesColor1..5
3. Render

Expected
All six segments take palette colours, or the five cycle.

Actual
The sixth segment renders in a default green that belongs to no configured palette, which quietly breaks a themed chart.

Context
Minor, but it is invisible until you look closely at a rendered chart — nothing warns that a series has run past the available colours.

Environment
App version: 8.8.0
Platform: Windows 11 Pro 10.0.26200