lib/gshadow.c: Use XREALLOC() instead of silently continuing on ENOMEM

We should do better, and correctly handle errors, since this is library
code.  However, I'm lazy right now, so let's die hard, and let us
improve this later.

Link: <https://github.com/shadow-maint/shadow/pull/991#discussion_r1660308154>
Reported-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

lib/gshadow.c

@@ -19,6 +19,7 @@
 
 #include "alloc/malloc.h"
 #include "alloc/realloc.h"
+#include "alloc/x/xrealloc.h"
 #include "prototypes.h"
 #include "defines.h"
 
@@ -38,20 +39,14 @@ static /*@null@*/char **build_list (char *s, char **list[], size_t * nlist)
 	size_t nelem = *nlist, size;
 
 	while (s != NULL && *s != '\0') {
-		ptr = REALLOC(*list, nelem + 1, char *);
-		if (ptr == NULL)
-			return NULL;
-
+		ptr = XREALLOC(*list, nelem + 1, char *);
 		ptr[nelem] = strsep(&s, ",");
 		nelem++;
 		*list = ptr;
 		*nlist = nelem;
 	}
 
-	ptr = REALLOC(*list, nelem + 1, char *);
-	if (ptr == NULL)
-		return NULL;
-
+	ptr = XREALLOC(*list, nelem + 1, char *);
 	ptr[nelem] = NULL;
 	*list = ptr;