outputorderwatcher: ignore outputs without crtc
when turning outputs **off** using `xrandr --off` that output is still connected but won't have any crtc attached. this is distinctly different from when kscreen disables an output, which indeed marks the output disconnected but it still has a crtc previously we would expect to find screens without crtc in the list of `qApp->screens()` which would then trigger an infinite refresh loop via the refresh timer because the screen would never be `present` on account of being off. BUG: 466362