Formatted numeric parts incorrectly handled

[anba]

Two issues:

1. PartitionDurationFormatPattern, step 4.e.i:

   4.e.i. Append FormatNumericUnits(durationFormat, duration, unit, signDisplayed) to result.

This step doesn't handle the case when FormatNumericUnits returns an empty list.

Instead something like:

4.e.i. Let numericPartsList be FormatNumericUnits(durationFormat, duration, unit, signDisplayed). 4.e.ii. If numericPartsList is not empty, append numericPartsList to result.

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2. FormatNumericUnits appends formatted elements to numericPartsList instead of using list-concatenation.

16.b. Append FormatNumericHours(durationFormat, hoursValue, signDisplayed) to numericPartsList.

Needs to be:

16.b. Let hoursParts be FormatNumericHours(durationFormat, hoursValue, signDisplayed). 16.c. Set numericPartsList to the list-concatenation of numericPartsList and hoursParts.

Same goes for the calls to FormatNumericMinutes and FormatNumericSeconds.

[ben-allen]

Thanks for these! I'm putting up a PR with commits resolving each of the issues you've identified right now.