Add another workaround for darwin SDL blank window bug

As for me it's much better then moving window at one pixel

(Based on the https://github.com/Noofbiz/glfwMojaveFix)

gui/darwin_opengl.go

@@ -0,0 +1,28 @@
+//+build darwin
+
+package gui
+
+/*
+#cgo darwin CFLAGS: -x objective-c -Wno-deprecated-declarations
+#cgo darwin LDFLAGS: -framework Foundation
+#include <Cocoa/Cocoa.h>
+void cocoa_update_nsgl_context(void* id) {
+    NSOpenGLContext *ctx = id;
+    [ctx update];
+}
+*/
+import "C"
+import (
+	"github.com/go-gl/glfw/v3.2/glfw"
+	"unsafe"
+)
+
+var nsglContextUpdateCounter int
+
+func UpdateNSGLContext(window *glfw.Window) {
+	if nsglContextUpdateCounter < 2 {
+		ctx := window.GetNSGLContext()
+		C.cocoa_update_nsgl_context(unsafe.Pointer(ctx))
+		nsglContextUpdateCounter++
+	}
+}

gui/gui.go

@@ -215,8 +215,6 @@ func (gui *GUI) Render() error {
 	startTime := time.Now()
 	showMessage := true
 
-	darwinRenderFixRequired := runtime.GOOS == "darwin"
-
 	for !gui.window.ShouldClose() {
 
 		select {
@@ -269,14 +267,7 @@ Buffer Size: %d lines
 				}
 			}
 
-			gui.window.SwapBuffers()
-
-			// Workaround for https://github.com/glfw/glfw/issues/1334
-			if darwinRenderFixRequired {
-				darwinRenderFixRequired = false
-				x, y := gui.window.GetPos()
-				gui.window.SetPos(x+1, y)
-			}
+			gui.SwapBuffers()
 		}
 
 	}
@@ -487,3 +478,8 @@ func (gui *GUI) launchTarget(target string) {
 		gui.logger.Errorf("Failed to launch external command %s: %s", cmd, err)
 	}
 }
+
+func (gui *GUI) SwapBuffers() {
+	UpdateNSGLContext(gui.window)
+	gui.window.SwapBuffers()
+}

gui/opengl.go

@@ -0,0 +1,9 @@
+// +build !darwin
+
+package gui
+
+import "github.com/go-gl/glfw/v3.2/glfw"
+
+func UpdateNSGLContext(window *glfw.Window) {
+
+}