Editorial: Don't override already existing timeZoneName in Intl options

The intention here was to set a default, not override any existing value.
Thanks to Anba for spotting this.

Closes: #3064

spec/intl.html

@@ -868,7 +868,7 @@ <h1>
             1. If _anyPresent_ is *true* and _inherit_ is ~relevant~, return *null*.
             1. For each property name _prop_ of _defaultOptions_, do
               1. Set _formatOptions_.[[&lt;_prop_>]] to *"numeric"*.
-            1. If _defaults_ is ~zoned-date-time~, then
+            1. If _defaults_ is ~zoned-date-time~ and _formatOptions_.[[timeZoneName]] is *undefined*, then
               1. Set _formatOptions_.[[timeZoneName]] to *"short"*.
           1. If _matcher_ is *"basic"*, then
             1. Let _bestFormat_ be BasicFormatMatcher(_formatOptions_, _formats_).