Electron: Cannot log out when you have unsynced notes

[belcherj]

On OSX and Linux in the electron app when you have unsynced notes try loggin out. I clicked delete notes and nothing happens.

[rachelmcr]

I tried this on macOS 10.15.4 with Electron v. 1.17.0-beta1. I had unsynced notes and received this prompt:

I selected "Delete Notes" and was logged out of the app.

I'll leave the issue open since I haven't tested Linux yet, but at least on OSX it seems to be working as expected.

[dmsnell]

Should have been resolved by #2066, specifically in 32dad4d.

This was broken during an Electron API change in v6.0.0
In version 1.7.11, which was in use at the time of #702 when we
started showing the message box, the dialog returned a number
to the provided callback for the response value.

When we updated in #1771 we failed to catch the breakage.