Steps to repro:

1. Open attached project and 't1' scene;
2. Select 'Area Light' gameobject in the Hierarchy;
3. Observe Area light's 'Range' field value in the Inspector.

Actual result:
Range value shows 'NaN'. See attached actual.png screesnhot.

Expected result:
'Range' value shows '0', if light's intensity is 0.

Notes:
- Reproducible in 2018.3.0a7, 2018.2.2f1, 2018.1.9f1;
- Reproducible on Windows 10 and OSX 10.13.6.