Editorial: "languageDisplay" can be undefined in Intl.DisplayNames.prototype.resolvedOptions

The [[LanguageDisplay]] slot can be `undefined`, so the assertion needs
to be changed to an If-step.

Author: anba

spec/displaynames.html

@@ -136,8 +136,8 @@ <h1>Intl.DisplayNames.prototype.resolvedOptions ( )</h1>
         1. For each row of <emu-xref href="#table-displaynames-resolvedoptions-properties"></emu-xref>, except the header row, in table order, do
           1. Let _p_ be the Property value of the current row.
           1. Let _v_ be the value of _displayNames_'s internal slot whose name is the Internal Slot value of the current row.
-          1. Assert: _v_ is not *undefined*.
-          1. Perform ! CreateDataPropertyOrThrow(_options_, _p_, _v_).
+          1. If _v_ is not *undefined*, then
+            1. Perform ! CreateDataPropertyOrThrow(_options_, _p_, _v_).
         1. Return _options_.
       </emu-alg>