patch 9.1.1581: possible memory leak in vim9generics.c

Problem:  possible memory leak in vim9generics.c
Solution: Free ret_free if ga_grow() fails and before returning
          (Lidong Yan).

In parse_generic_func_type_args() at vim9generics.c, we allocate memory
in ret_name and should free it by calling vim_free(ret_free). If
ga_grow on gfatab->gfat_args failed, we forget to call vim_free(ret_free)
thus would cause a leak. Add vim_free(ret_free) before return NULL.

closes: #17821

Signed-off-by: Lidong Yan <yldhome2d2@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/version.c

@@ -719,6 +719,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1581,
 /**/
     1580,
 /**/