Full-Screen Switch Does Nothing When Using SDL

When using SDL switches, e.g.

-sdl -full-screen -display sdl

... you'd expect the display to start full-screen, as per the switch description, but it just starts in a window. Pressing the full-screen key combination (Ctrl+Alt+F) enters fullscreen mode as expected.

Tested on QEmu 2.12.0 using qemu-system-x86_64.