How to reproduce:
1. Create a new project
2. Go to Menu -> Edit -> Project Settings -> Editor -> Set Version Control Mode to use Perforce
3. Go to Menu -> Window -> Rendering -> Lighting settings -> uncheck Auto Generate and click Generate Lightning
4. Add and submit files in to perforce
5. Go to -> Project Settings -> Editor -> Set Version Control -> enable Work Offline
6. Disable your internet and try to generate light again

Expected: It is possible to Generate Light in offline mode
Actual: Errors are spammed in the Console window and Generate Lightning job is never finished

Reproduced on: 2018.3.3f1, 2019.1.0a14, 2019.2.0a1

Note: In versions from 2018.3.0a1 to 2018.2.0a10 and from 2019.1.0a1 to 2019.1.0a8 only one error pops up: "Cannot delete files in offline mode"