address issue where dispatch_io_read cal be called with a data argume…

[mdejong]

Hello. I ran into a crash in the block passed to dispatch_io_read and from what I could see it seemed to be caused by data being set to nil. This is my attempt to address that crash by setting dataSize to 0. This seemed to be a random one time situation and I have not been able to reproduce the issue since.

[mdejong]

FYI, the done flag was true when this crash was hit. The stack trace looked like this:

* thread #7, queue = 'com.apple.libdispatch-io.opq', stop reason = EXC_BAD_ACCESS (code=1, address=0x30)
frame #0: 0x000000018142c480 libdispatch.dylib`dispatch_data_get_size
* frame #1: 0x00000001010af560 ___`__53-[PTProtocol readPayloadOfSize:overChannel:callback:]_block_invoke(.block_descriptor=0x00000002820588a0, done=true, data=0x0000000000000000, error=57) at PTProtocol.m:247:23
frame #2: 0x000000018142be44 libdispatch.dylib`___dispatch_operation_deliver_data_block_invoke + 148