added isset-check to prevent the errors in issue #34

[lduer]

I've added some check if vars and array-keys exist to prevent the errors thrown in #34

Reason for the errors is the GET-parameter ?[...]&action=update[...] which is not always added to the ajax-request to checks.php. In this case, the request-url doesn't request all data and the so the response array misses e.g. the timezone-key.

[yylzcom]

Hi, after I applying your code, there is an error shows "NaN hours, NaN Mins" on the duration.
Please check and help me solve this problem