fix: V-002 security vulnerability

Automated security fix generated by OrbisAI Security

src/realpath.c

@@ -21,6 +21,7 @@ int realpath_builtin(WORD_LIST *list)
 		} else {
 			printf("%s\n", realbuf);
 			free(realbuf);
+			realbuf = NULL;
 		}
 	}
 	return es;