BUG: stats cache json file not processed properly for small datasets

[jqnatividad]

stats has a default --cache-threshold of 5000 milliseconds - only creating a stats cache if it takes more than 5 seconds to compute stats for a file.

For small files or very fast computers however, this threshold was rarely reached and the current stats caching logic was bubbling up stats.json does not exist "errors" that was causing qsv to exit, though they should have been ignored.

CI did not catch this as the "false error" only showed up whenever stats tries to check the stats.json file file on the subsequent runs.