Make auditor only run json.dumps if we're going to dump state to file

Commit 77f5b201248c0684d87289540d3f94873f5c5e38 introduced logic to throttle writing the status file to once per minute. However, it still ran json.dumps and potentially utf8 conversion on every call. We have identified that this uses a lot of CPU, only to throw the string away.

This change only calls json.dumps if we're going to write the state to file.