Add GLFW_NO_API for creating context-less windows

src/wgl_context.c

@@ -672,6 +672,13 @@ GLFWAPI HGLRC glfwGetWGLContext(GLFWwindow* handle)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;
     _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    if (window->context.api == GLFW_NO_API)
+    {
+        _glfwInputError(GLFW_NO_WINDOW_CONTEXT, NULL);
+        return NULL;
+    }
+
     return window->wgl.context;
 }