allow empty json reports instead of failing

[lenntt]

Fixes #47

Specifically check for empty json and not ignoring all invalid json, because in some cases, you just want to see something is wrong.

[coveralls]

Coverage increased (+0.01%) to 98.667% when pulling bb3556a on lenntt:47_emptyjson into 8e20dda on wswebcreation:master.

[wswebcreation]

Good job man, tnx. Will make a new version