IMShow throws error when called in GoRoutine on OSX Catilina

[ipeerbhai]

IMShow throws an NSException if called in a GoRoutine.

Description

When calling IMShow in a GoRoutine on OSX, get the following exception: Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'NSWindow drag regions should only be invalidated on the Main Thread!'

Steps to Reproduce

I've attached a file that repros the issue consistently. Just run it.

Your Environment

• Operating System and version: OSX Catalina 10.15.2
• OpenCV version used: 4.1.2
• How did you install OpenCV? Brew
• GoCV version used: 0.22.0
• Go version: 1.13
• Did you run the env.sh or env.cmd script before trying to go run or go build? No main.go.zip