TST: corner_case for read_csv with usecols GH5766
BUG: regression in read_csv parser handling of usecols GH5766

GH4406 fixed one bug and introduced (exposed?) this corner case
where the loop over columns continues even after all usecols
have been fulfilled, causing an out-of-bound lookup in names.
Merge pull request #5770 from y-p/GH5766

BUG: regression in read_csv parser handling of usecols GH5766