uwrap: 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/uid_wrapper.c b/src/uid_wrapper.c
index f04642a..dd87da4 100644
--- a/src/uid_wrapper.c
+++ b/src/uid_wrapper.c
@@ -2453,7 +2453,11 @@ void uwrap_destructor(void)
 	}
 
 
-	if (uwrap.libc.handle != NULL) {
+	if (uwrap.libc.handle != NULL
+#ifdef RTLD_NEXT
+		&& uwrap.libc.handle != RTLD_NEXT
+#endif
+			) {
 		dlclose(uwrap.libc.handle);
 	}