Avoid json decode error if validation output josn is empty

[jdhayhurst]

It is possible for the json output file (from the validation process) to have not been written before the job is terminated by the LSF/Nextflow. When evaluating these json outputs (

gwas-sumstats-service/sumstats_service/resources/api_utils.py

Line 163 in 68ae30e

results["validationList"].append(json.load(f))

) if the json is empty, it throws an error:

json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

This causes the validation to hang, so we should write something to handle (ignore) this error.

[jdhayhurst]

this is an issue