Update GCD/GCDAsyncSocket.m

Fix bugs that prevent the socket from reading any data when the following settings are used to avoid linking with SSL:
#define IS_SECURE_TRANSPORT_AVAILABLE      NO
#define SECURE_TRANSPORT_MAYBE_AVAILABLE   0
#define SECURE_TRANSPORT_MAYBE_UNAVAILABLE 1
Merge branch 'patch-1' of https://github.com/ercollin/CocoaAsyncSocket into ercollin-patch-1

Conflicts:
	GCD/GCDAsyncSocket.m
GCDAsyncSocket: fixed bug: socket was closed with nil error if SecureTransport is unavaliable.

In case if IS_SECURE_TRANSPORT_AVAILABLE == NO, in 'doReadEOF' method code for creating
connectionClosedError wasn't called.