wayland/outputs: Fix potential crash when output has no monitor [43]
Backport of !2827 (merged) to 43, which had the wl_output_v3 code with the bug backported in 43.2. See gnome-shell#6740 (closed).
Backport of !2827 (merged) to 43, which had the wl_output_v3 code with the bug backported in 43.2. See gnome-shell#6740 (closed).