don't try IPv6 on windows if it's not installed

ChangeLog

@@ -54,6 +54,7 @@ release 0.14.3
 	* fixed CIDR-distance calculation in the precense of IPv6 peers
 	* save partial resume data for torrents that are queued for checking
 	  or checking, to maintain stats and renamed files
+	* Don't try IPv6 on windows if it's not installed
 
 release 0.14.2
 

src/session_impl.cpp

@@ -725,6 +725,15 @@ namespace aux {
 				async_accept(s.sock);
 			}
 
+#ifdef TORRENT_WINDOWS
+			// only try to open the IPv6 port if IPv6 is installed
+			SOCKADDR_STORAGE storage;
+			int len = sizeof(storage);
+			if (WSAStringToAddressA("::1", AF_INET6, 0,
+				(sockaddr*)&storage, &len) != SOCKET_ERROR)
+			{
+#endif
+
 			s = setup_listener(
 				tcp::endpoint(address_v6::any(), m_listen_interface.port())
 				, m_listen_port_retries, true);
@@ -734,6 +743,9 @@ namespace aux {
 				m_listen_sockets.push_back(s);
 				async_accept(s.sock);
 			}
+#ifdef TORRENT_WINDOWS
+			}
+#endif
 		}
 		else
 		{