xgetXXbyYY: tfix

It seems obvious that it was a typo.

Link: <https://github.com/shadow-maint/shadow/pull/729#discussion_r1207551013>
Fixes: e73a2194b3 ("xgetXXbyYY: Handle DUP_FUNCTION failure")
Cc: Samanta Navarro <ferivoz@riseup.net>
Cc: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

libmisc/xgetXXbyYY.c

@@ -69,7 +69,7 @@
 			/* Build a result structure that can be freed by
 			 * the shadow *_free functions. */
 			LOOKUP_TYPE *ret_result = DUP_FUNCTION(result);
-			if (NULL == result) {
+			if (NULL == ret_result) {
 				fprintf (log_get_logfd(),
 				         _("%s: out of memory\n"),
 				         "x" STRINGIZE(FUNCTION_NAME));