[doc/async] Change StreamController.broadcast() doc according to the current behavior

Bug: #29403
Change-Id: I9ef53b3c4e039bdc84d4cdfa9e306efb6eb0ffba
CoreLibraryReviewExempt: Documentation-only change
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/340860
Reviewed-by: Lasse Nielsen <[email protected]>
Reviewed-by: Alexander Thomas <[email protected]>
Commit-Queue: Alexander Thomas <[email protected]>

Author: sgrekhov

sdk/lib/async/stream_controller.dart

@@ -134,8 +134,8 @@ abstract interface class StreamController<T> implements StreamSink<T> {
   /// listeners at the time when [add], [addError] or [close] is called.
   /// It is not allowed to call `add`, `addError`, or `close` before a previous
   /// call has returned. The controller does not have any internal queue of
-  /// events, and if there are no listeners at the time the event is added,
-  /// it will just be dropped, or, if it is an error, be reported as uncaught.
+  /// events, and if there are no listeners at the time the event or error is
+  /// added, it will just be dropped.
   ///
   /// Each listener subscription is handled independently,
   /// and if one pauses, only the pausing listener is affected.