Fix StreamSocketOutput

Author: benaadams

src/Microsoft.AspNet.Server.Kestrel/Filter/StreamSocketOutput.cs

@@ -52,7 +52,7 @@ public void ProducingComplete(MemoryPoolIterator2 end, int count)
                 returnBlock.Pool?.Return(returnBlock);
             }
 
-            _outputStream.Write(end.Block.Array, end.Block.Data.Offset, end.Index);
+            _outputStream.Write(end.Block.Array, end.Block.Data.Offset, end.Index - end.Block.Data.Offset);
             end.Block.Pool?.Return(end.Block);
         }
     }