app/internal/wm: [iOS] use proper constructor for gl.Functions

We're about to load OpenGL function pointers into gl.Function structs.
Make sure iOS internally uses the NewFunctions constructor, not just
new(Functions).

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

app/internal/wm/gl_ios.go

@@ -46,19 +46,28 @@ func newContext(w *window) (*context, error) {
 	if ctx == 0 {
 		return nil, fmt.Errorf("failed to create EAGLContext")
 	}
+	api := contextAPI()
+	f, err := gl.NewFunctions(api.Context)
+	if err != nil {
+		return nil, err
+	}
 	c := &context{
 		ctx:   ctx,
 		owner: w,
 		layer: C.CFTypeRef(w.contextLayer()),
-		c:     new(gl.Functions),
+		c:     f,
 	}
 	return c, nil
 }
 
-func (c *context) API() gpu.API {
+func contextAPI() gpu.OpenGL {
 	return gpu.OpenGL{}
 }
 
+func (c *context) API() gpu.API {
+	return contextAPI()
+}
+
 func (c *context) Release() {
 	if c.ctx == 0 {
 		return