package:objective_c v9.6.1

• Fix a crash in the NSInputStream returned by toNSInputStream: reading
  from or closing the stream after its Dart side had already closed it raised
  NSInternalInconsistencyException ("DartInputStreamAdapter:
  Dart_PostCObject_DL failed") and aborted the process. NSURLSession does
  exactly that with a request body stream when the request completes with an
  error or is cancelled right after it starts. close is now idempotent, and
  a read on a closed stream (or one whose Dart owner is gone) fails with -1
  instead of asserting.
• Fix a bug where toNSData/toNSMutableData added the returned NSData
  to the autorelease pool.
• Fix a bug where toNSInputStream would create cycles between Dart and
  Objective-C.