Fix `dunstctl rule` error when not providing rule state

[SeerLite]

Previously showed "line 130: 3: unbound variable" instead of the pretty error message.

[bynect]

So the problem was the reference to "${3}"?

[SeerLite]

Yes, the first commit just changes "$3" to "${3:-}" and second one replaces with the if with a case

[bynect]

Thanks 👍🏻

[zappolowski]

The issues comes from using set -u when there are not enough arguments provided. $3 is undefined and thus triggers the original error. ${3:-} uses the empty fallback in this case to avoid the issue.