Cant run examples, blank screen with SDL Error
Hello

I wanted to check out this project, installed the dependencies and i got this:
```bash
(ql:quickload :sketch-examples)
To load "sketch-examples":
  Load 1 ASDF system:
    sketch-examples
; Loading "sketch-examples"

(:SKETCH-EXAMPLES)
(make-instance 'sketch-examples:sinewave)

debugger invoked on a SDL2::SDL-RC-ERROR in thread
#<THREAD "SDL2 Main Thread" RUNNING {1001CA72C3}>:
  SDL Error (-1): That operation is not supported

The current thread is not at the foreground,
SB-THREAD:RELEASE-FOREGROUND has to be called in #<SB-THREAD:THREAD "main thread" RUNNING {1004DE01F3}>
```
I don't know what to do from here :(