Simplify check introduced in commit '6c9e4c05'

- Removed redundant part of check.
- Updated comment, elaborating on 'POLLHUP' omission in the check.

lib/mysql_data_stream.cpp

@@ -667,10 +667,10 @@ int MySQL_Data_Stream::read_from_net() {
 				proxy_debug(PROXY_DEBUG_NET, 5, "Session=%p, Datastream=%p -- SSL_get_error() is SSL_ERROR_SYSCALL, errno: %d\n", sess, this, errno);
 			} else {
 				if (r==0) { // we couldn't read any data
-					if ((revents & POLLIN) || ((revents & POLLIN) && (revents & POLLHUP))) {
+					if (revents & POLLIN) {
 						// If revents is holding either POLLIN, or POLLIN and POLLHUP, but 'recv()' returns 0,
-						// reading no data, the socket has been already closed by the peer. Second part of the
-						// check is obviously redundant, but is left for clarity on the cases being covered.
+						// reading no data, the socket has been already closed by the peer. Due to this we can
+						// ignore POLLHUP in this check, since we should reach here ONLY if POLLIN was set.
 						proxy_debug(PROXY_DEBUG_NET, 5, "Session=%p, Datastream=%p -- shutdown soft\n", sess, this);
 						shut_soft();
 					}