Fixed the logical size for rendering to texture, thanks to Mason Wheeler.

Mason Wheeler

The SDL_RenderGetLogicalSize function should always return the amount of pixels that are currently available for rendering to.  But after updating to the latest SDL2, I started getting crashes because it was returning (0,0) as the logical size!  After a bit of debugging, I tracked it down to the following code in SDL_SetRenderTarget:

    if (texture) {
        renderer->viewport.x = 0;
        renderer->viewport.y = 0;
        renderer->viewport.w = texture->w;
        renderer->viewport.h = texture->h;
        renderer->scale.x = 1.0f;
        renderer->scale.y = 1.0f;
        renderer->logical_w = 0;
        renderer->logical_h = 0;
    }

This is obviously wrong; 0 is never the correct value for a valid renderer.  Those last two lines should read:

        renderer->logical_w = texture->w;
        renderer->logical_h = texture->h;