read_sas() bug with SAS formats

[dwilson98-kermit]

read_sas() fails to appropriately process SAS formats that include negative values.
For example, if you have a .sas7bdat file with a single numeric variable named x with values -7, 1, and 2 and a SAS format catalog file that defines the format:

proc format;
value testf
-7="Missing"
1="Yes"
2="No"
;
run;

Then the attributes of dataframe$x show a value of -0.625 instead of -7.

``` r
library(haven)
bweights <- read_sas('C:/Test/test.sas7bdat', catalog_file='C:/Test/formats.sas7bcat')
attributes(bweights$x)
#> $format.sas
#> [1] "TESTF"
#> 
#> $class
#> [1] "haven_labelled" "vctrs_vctr"     "double"        
#> 
#> $labels
#> Missing     Yes      No 
#>  -0.625   1.000   2.000

[test.zip](https://github.com/user-attachments/files/18101365/test.zip)