Cook's distance, DFFITS, and DFBETAS always label at least one point

The functions `jcreg_cooksd`, `jcreg_dffits` and `jcreg_dfbetas` all have an argument `nLabels` which works fine unless `nLabels = 0`. If `nLabels` is set to zero, the functions still label one point. The problem has something to do with this line of code:
```
top_dff <- as.numeric(names(sort(abs(df_fits), decreasing = TRUE)[1:nLabels]))
```