AFNetworkPacketReadToWriteStream should close the write stream under error conditions

[keithduncan]

Original author: ke...@realmacsoftware.com (February 08, 2012 19:13:38)

Check that this packet closes its secondary stream under success, error, and deallocation conditions. We shouldn't hold the file open unnecessarily.

Original issue: http://code.google.com/p/amber-framework/issues/detail?id=56