zsh-completion: Some parameters may be specified multiple times
zsh-completion: Some parameters may be specified multiple times

--screen, --output and image parameters can be provided
multiple times for setting wallpapers of different displays.
This fixes zsh auto-completion for this use case.

Signed-off-by: Sebastian Reichel <1ea78bda3cb6d36efdb8fc89aad6555e21b4887e@ring0.de>

stoeckmann/xwallpaper,stoeckmann/xwallpaper