--d4 Creates d4 files with inf/NaN values
Been doing some work in the d4 repo and wanted to compare d4 files made using `d4tools create` and `mosdepth`. However with the small BAMs I've been testing with, `mosdepth` created d4 files have inf/NaN values for depth. Not sure if this is an issue with d4 or mosdepth.

**Mosdepth versions tested:** `0.3.6` (from conda) and `0.3.8` (the `mosdepth_d4` binary in the releases page)

d4tools was built from source in a fresh clone of the repo. 

**d4tools create**
```
> d4tools create -Azr ../data/genome.fna.fai ../data/test.bam test.d4
> d4tools show test.d4 > show.out
> head show.out
NC_052520.2	0	116790	0
NC_052520.2	116790	116942	1
NC_052520.2	116942	116946	0
NC_052520.2	116946	117093	1
NC_052520.2	117093	138700	0
NC_052520.2	138700	138848	1
NC_052520.2	138848	138852	2
NC_052520.2	138852	139000	1
NC_052520.2	139000	225154	0
NC_052520.2	225154	225306	1
```

**mosdepth 0.3.6**
```
> mosdepth --d4 test ../data/test.bam
> d4tools show test.per-base.d4 > show.out
> head show.out
NC_052520.2	0	36240	NaN
NC_052520.2	36240	36391	inf
NC_052520.2	36391	36426	NaN
NC_052520.2	36426	36577	inf
NC_052520.2	36577	43701	NaN
NC_052520.2	43701	43971	inf
NC_052520.2	43971	116790	NaN
NC_052520.2	116790	116941	inf
NC_052520.2	116941	116946	NaN
NC_052520.2	116946	117092	inf
```

0.3.8 is the same output as 0.3.6, no need to show it here.

Attached zipped folder of all the files for reference. 
[mosdepth-test.zip](https://github.com/user-attachments/files/16678568/mosdepth-test.zip)
