app,app/internal/wm: release OpenGL context after use

Otherwise, making a context current on another thread may result in
an EGL_BAD_ACCESS error.

Fixes gio#248

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/loop.go

@@ -69,6 +69,7 @@ func (l *renderLoop) renderLoop(ctx wm.Context) error {
 			initErr <- err
 			return
 		}
+		defer ctx.ReleaseCurrent()
 		g, err := gpu.New(ctx.API())
 		if err != nil {
 			initErr <- err