To reproduce:
1. Open any project
2. Create a script and add it to GameObject
3. Close the project
4. Move the created script outside the scope of Assets folder
5. Reopen the project and check the Inspector of the GameObject (that script was attached to)

Expected: missing script component allows to locate the script via object picker
Actual: missing script component's object picker is grayed out

Reproduced in: 2019.1.0a11, 2019.1.0a15, 2019.2.0a2
Not reproduced in: 2017.4.19f1, 2018.3.3f1, 2019.1.0a10

Note: reproduces on Mac and Windows, (not tested on Linux)