Conditionally reject ready promise

Author: vmpstr

css-view-transitions-1/Overview.bs

@@ -850,7 +850,7 @@ The {{ViewTransition/domUpdated}} [=getter steps=] are to return [=this's=] [=Vi
 
     1. Set |document|'s [=document/active DOM transition=] to null.
 
-    1. [=Reject=] |transition|'s [=ViewTransition/ready promise=] with |reason|.
+    1. If |transition|'s [=ViewTransition/ready promise=] has not yet been resolved, [=reject=] it with |reason|.
 
     1. [=Reject=] |transition|'s [=ViewTransition/finished promise=] with |reason|.
 </div>