fix bad merge of DoAndWait PR

Author: dweymouth

internal/driver/glfw/loop.go

@@ -170,13 +170,14 @@ func (d *gLDriver) runSingleFrame() (exit, animationsDone bool) {
 		select {
 		case f := <-funcQueue.Out():
 			f.f()
-			f.done <- struct{}{}
+			if f.done != nil {
+				f.done <- struct{}{}
+			}
 		default:
 			funcsDone = true
 		}
 	}
 
-
 	// apply settings change if any
 	settingsMutex.Lock()
 	set := settingsToApply