Editorial: Handle absent options in DifferenceZonedDateTime

Author: anba

spec/zoneddatetime.html

@@ -1271,6 +1271,8 @@ <h1>
         </dd>
       </dl>
       <emu-alg>
+        1. If _options_ is not present, set _options_ to *undefined*.
+        1. Assert: Type(_options_) is Object or Undefined.
         1. If _ns1_ is _ns2_, then
           1. Return ! CreateDurationRecord(0, 0, 0, 0, 0, 0, 0, 0, 0, 0).
         1. Let _startInstant_ be ! CreateTemporalInstant(_ns1_).