Bad error message for unaccounted for COMID

Need to fix the error handling for a request like this 
```
sc_get_data(comid='10850240', metric='clay',aoi='cat,ws')
```

```
Error in `dplyr::select()` at StreamCatTools/R/sc_get_data.R:175:9:
! `select()` doesn't handle lists.
Run `rlang::last_trace()` to see where the error occurred.
```