Fix warning on MinGW and MSVC12
diff --git a/library/net.c b/library/net.c
index 3e14466..6333b0f 100644
--- a/library/net.c
+++ b/library/net.c
@@ -223,6 +223,7 @@
  */
 static int net_would_block( int fd )
 {
+    ((void) fd);
     return( WSAGetLastError() == WSAEWOULDBLOCK );
 }
 #else