core: Don't leak memory if error is unknown

If error is unknown, the "return 1" call was not freeing error which was
malloced at the beginning of the function.
diff --git a/options.c b/options.c
index 6462c67..1c44f42 100644
--- a/options.c
+++ b/options.c
@@ -271,6 +271,7 @@
 		if (!error[i]) {
 			log_err("Unknown error %s, please use number value \n",
 				  fname);
+			free(error);
 			return 1;
 		}
 		i++;