Fixes color choice layout issue.

Color theme picker size calculation had a bug that caused incorrect column count after scrolling through all pages of choices.

Before: http://screen/BZdSY8NLSUTiz4z
After: http://screen/4hAF2UpX2nsYrrH

Bug: 248080123
Test: TreeHugger
Change-Id: Ia17b03d9b1eaa1b102072fa201cae033222199f7