Calibrating a very old date fails with an uninformative error message

``` r
library(c14)
c14_calibrate(80000, 100)
#>
#> [1] c. 55000 cal BP

c14_calibrate(85000, 100)
#> Error:
#> ℹ In index: 1.
#> Caused by error in `colnames<-`:
#> ! attempt to set 'colnames' on an object with less than two dimensions

c14_calibrate(90000, 100)
#> Warning in min(above): no non-missing arguments to min; returning Inf
#> Warning in max(above): no non-missing arguments to max; returning -Inf
#> Error:
#> ℹ In index: 1.
#> Caused by error in `min(above):max(above)`:
#> ! result would be too long a vector
```

^{Created on 2024-12-01 with [reprex v2.1.1](https://reprex.tidyverse.org)}

I would be better to return `NA` with an informative warning.