internal/uidriver/glfw: Bug fix: Rendering should be updated after restoring from fullscreen
internal/uidriver/glfw: Bug fix: Rendering should be updated after restoring from fullscreen

u.toChangeSize affects the result of u.updateSize. When the callback
for WindowSetSize is invoked, toChangeSize should be true.

In order to simplify the logic, we have to remove toChangeSize later.

Closes #1884

hajimehoshi/ebiten,hajimehoshi/ebiten