pvt_twitter fails when using fetch_classic

Getting the bug

```r
r$> pvt_twitter(auth, locations = "CA", epiweeks = epirange(201501, 202001)) %>% fetch_classic
Error in if (info$name %in% columns) { : argument is of length zero
r$> traceback()
3: parse_data_frame(epidata_call, m$epidata, disable_date_parsing = disable_date_parsing)
2: fetch_classic(.)
1: pvt_twitter(...)
```