Fixes New Structure issues in test/extensions/ColumnHider

In cases where the column config changes lookup by columnId can fail, so when
this happens we just grab the first column and try again.

When there's no rows at all (e.g. Recreate Grid was called) we don't bother
trying to set focus.

I traced the breakage back to commit c632766. I wasn't exactly sure of the
best way to handle focus in these odd cases but this approach seemed decent.