💥 Do not crash on empty pseudo arguments

[bartveneman]

Ran into ::view-transition-old() in the wild and added some more resilience while I was fixing it. This aligns with previous fixes in #14 and #29.

The complete code as I found it:

html::view-transition-old() {
	animation-name: -ua-view-transition-fade-out;
}

html::view-transition-new() {
	animation-name: -ua-view-transition-fade-in;
}

[bramus]

Some minor code optimization suggestions