When overridden in a derived class, gets a value indicating whether the current stream supports writing.
true if the stream supports writing; otherwise, false.
If a class derived from System.IO.Stream does not support writing, a call to Stream.Write(Byte[], int, int), Stream.BeginWrite(Byte[], int, int, AsyncCallback, object), or Stream.WriteByte(byte) throws a NotSupportedException.
If the stream is closed, this property returns false.