Dynamically changing HiDPI awareness does not trigger content callback

Steps to reproduce:

```
// 1. set a window content scale callback
  glfwSetWindowContentScaleCallback(fWindow, callbacks::onContentScaleChange);

// here we assume content scale is 2.0

// 2. change HiDPI awareness
  glfwSetWindowAttrib(fWindow, GLFW_SCALE_FRAMEBUFFER,  GLFW_FALSE);

// here content scale is 1.0 but callback is not called
```

The callback is not called.