json output can be invalid, sometimes it produces NaN

[cariaso]

minor but worthy of note

https://stackoverflow.com/questions/6601812/sending-nan-in-json
https://stackoverflow.com/questions/72363350/how-to-adapt-json-parser-for-nan-in-javascript

{"samplename": {
"Coverage_MAD": NaN, 
"Median_depth": NaN, 
"Total_CN": null, 
"Spacer_CN": null, 
"Total_CN_raw": NaN, 
"Spacer_CN_raw": NaN, 
"Variants_called": null, 
...

should instead be

{
  "samplename": {
    "Coverage_MAD": null,
    "Median_depth": null,
    "Total_CN": null,
    "Spacer_CN": null,
    "Total_CN_raw": null,
    "Spacer_CN_raw": null, 
    "Variants_called": null, 
```