fix broken auto-width columns

This fixes a regression introduced by
f552402f1f0576df9f0436868bf0b4987468f0e9
fix extra width added to percent columns past grid width

When there is extra width left over after calculating column
widths this logic error could allow extra pixels to be added
on percent width columns that could exceed the available width.
Merge pull request #1946 from Envisage/master

fix broken auto-width columns