nwrap: 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/nss_wrapper.c b/src/nss_wrapper.c
index 07c9757..b95afdf 100644
--- a/src/nss_wrapper.c
+++ b/src/nss_wrapper.c
@@ -6499,13 +6499,25 @@ void nwrap_destructor(void)
 
 		/* libc */
 		if (m->libc != NULL) {
-			if (m->libc->handle != NULL) {
+			if (m->libc->handle != NULL
+#ifdef RTLD_NEXT
+				&& m->libc->handle != RTLD_NEXT
+#endif
+					) {
 				dlclose(m->libc->handle);
 			}
-			if (m->libc->nsl_handle != NULL) {
+			if (m->libc->nsl_handle != NULL
+#ifdef RTLD_NEXT
+				&& m->libc->nsl_handle != RTLD_NEXT
+#endif
+					) {
 				dlclose(m->libc->nsl_handle);
 			}
-			if (m->libc->sock_handle != NULL) {
+			if (m->libc->sock_handle != NULL
+#ifdef RTLD_NEXT
+				&& m->libc->sock_handle != RTLD_NEXT
+#endif
+					) {
 				dlclose(m->libc->sock_handle);
 			}
 			SAFE_FREE(m->libc);