ebiten: Bug fix: The vertex backend was not flushed when the screen is shrunk
ebiten: Bug fix: The vertex backend was not flushed when the screen is shrunk

The last parameter of QuadVertices represents whether we can flush
the backend vertices (on Wasm). The problem was that this was
unexpectedly false even though the image is the screen, when the
screen rendering is done with FilterLinear instead of FilterScreen.

Closes #1479

hajimehoshi/ebiten,hajimehoshi/ebiten