media_player: only add a separating colon if there is a valid prefix and suffix

[jackwilsdon]

This PR changes the media player entity row to only add a colon separator to the status line when there is both a prefix and a suffix.

This issue affected my Sonos device, displaying a colon when there is nothing playing (and also when using TTS);

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This change only affects the Lovelace UI.

[jackwilsdon]

I do have one note; I could condense this logic here;

https://github.com/home-assistant/home-assistant-polymer/blob/fdceb9dc52c985903b6f742852e7e9ef1fa49bb5/src/panels/lovelace/entity-rows/hui-media-player-entity-row.js#L126-L139

By changing it to something like this;

    if (prefix && suffix) {
      return `${prefix}: ${suffix}`;
    }

    // Return the concatenated prefix and suffix, using an empty string if either are missing.
    return (prefix || "") + (suffix || "");

But I'm not sure if that is as clear / expressive of what it's trying to achieve.

[jackwilsdon]

It looks like this PR also fixes the "undefined" issue I've been having on my Apple TV;

Old	New

[zsarnett]

This is Much cleaner now. Great Job!

[jackwilsdon]

Cheers!