Delete undefined key triggers error

[swedmike]

Running a delete on urlOptions[label][attr] at line 1559 triggers an undefined error if the label is not there, which will stop JS execution and thus show the processindicator forever, making the table unusable.

The fix is obviously a small check:

if ("label" in urlOptions && "attr" in urlOptions[label]) {
  delete urlOptions[label][attr];
}