swrap: Avoid dclose(RTLD_NEXT)

In case the libc was not found and RTLD_NEXT is used instead, we should not
dlclose it, otherwise mayhem happens.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

diff --git a/src/socket_wrapper.c b/src/socket_wrapper.c
index ec8321f..cc9e17d 100644
--- a/src/socket_wrapper.c
+++ b/src/socket_wrapper.c
@@ -7831,10 +7831,18 @@ void swrap_destructor(void)
 
 	SAFE_FREE(sockets);
 
-	if (swrap.libc.handle != NULL) {
+	if (swrap.libc.handle != NULL
+#ifdef RTLD_NEXT
+		&& swrap.libc.handle != RTLD_NEXT
+#endif
+			) {
 		dlclose(swrap.libc.handle);
 	}
-	if (swrap.libc.socket_handle) {
+	if (swrap.libc.socket_handle
+#ifdef RTLD_NEXT
+		&& swrap.libc.socket_handle != RTLD_NEXT
+#endif
+			) {
 		dlclose(swrap.libc.socket_handle);
 	}
 }