Fix handle connection reset during session init

Patch to handle nmap version probes.
Signed-off-by: Dhammika Pathirana <dhammika@gmail.com>

src/decoder.hpp

@@ -91,6 +91,10 @@ namespace zmq
         //  bytes actually processed.
         inline size_t process_buffer (unsigned char *data_, size_t size_)
         {
+            //  Check if we had an error in previous attempt.
+            if (unlikely (!(static_cast <T*> (this)->next)))
+                return (size_t) -1;
+
             //  In case of zero-copy simply adjust the pointers, no copying
             //  is required. Also, run the state machine in case all the data
             //  were processed.

src/zmq_engine.cpp

@@ -151,7 +151,7 @@ void zmq::zmq_engine_t::in_event ()
         inout->flush ();
     }
 
-    if (disconnection)
+    if (inout && disconnection)
         error ();
 }