Default of current-time-display is broken

[heff]

Follow up on #74

The same is true for other time-display elements.

Before #74 https://media-chrome-djevl3pei-mux.vercel.app/examples/control-elements/media-current-time-display.html

After https://media-chrome-err0093s8-mux.vercel.app/examples/control-elements/media-current-time-display.html

[cjpillsbury]

Unrelated to #74 . See: https://media-chrome.mux.dev/examples/control-elements/media-time-display.html Still good as a followup if we want to re-introduce default values (consideration: -:-- or similar instead to make clear that no value has been set?)

[heff]

Hmm, not sure where we lost that default then. But yeah, we should fix that. I like -:--.

[luwes]

Just checked, this is still a bug