return eagain if nread is 0 per libuv (#100)

Suppress EAGAIN/EWOULDBLOCK equivalents.

src/uvw/stream.hpp

@@ -141,6 +141,10 @@ class StreamHandle: public Handle<T, U> {
         } else if(nread > 0) {
             // data available
             ref.publish(DataEvent{std::move(data), static_cast<std::size_t>(nread)});
+        } else if(nread == 0) {
+            // equivalent to EAGAIN/EWOULDBLOCK
+            // http://docs.libuv.org/en/v1.x/stream.html
+            // simply catch this condition and do not publish an event
         } else {
             // transmission error
             ref.publish(ErrorEvent(nread));