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/internal/wm/d3d11_windows.go

@@ -117,6 +117,8 @@ func (c *d3d11Context) MakeCurrent() error {
 	return nil
 }
 
+func (c *d3d11Context) ReleaseCurrent() {}
+
 func (c *d3d11Context) Lock() {}
 
 func (c *d3d11Context) Unlock() {}