Editor gets closed and freezes on error pop up, when an already opened scene which is in another project is double-clicked from explorer.

Steps to repro:
1. Create two projects (Ex: P1 and P2) with at least one scene in each.
2. Open Project P1 and P2 with same unity version.
2. Double click unity scene from P2/P1 in file explorer/finder.
3. "About to open another unity project" > Click Open.
4. Error: -"Multiple unity instances cannot open the same project" > OK

Actual Result:
1. Freez on Error PopUp
2. Unity Editor launcher is open
3. One project gets closed.

Expected Result:
An editor does not freezes on clicking error pop-up.

Environment:
Only Mac

Occurring with:
2019.2.0a14, 2019.2.0a5

Working with:
2019.2.0a4

Note: 1. Closing launcher closes the error pop-up as well as the project.
2. In 2019.3.0a1 "About to open another unity project" pop-up is not shown.