Merge branch 'jc/maint-1.6.4-show-branch-default' into maint

* jc/maint-1.6.4-show-branch-default:
show-branch: fix segfault when showbranch.default exists

diff --cc builtin-show-branch.c
index 01bea3b583b53f4930a1ab17d64b1b714f58099c,5d85ab0cae9029f9324fca9a9923e8b61b751607..baec9ed56f4098183445b85cdd1b2789d487d6fe
--- 1/builtin-show-branch.c
--- 2/builtin-show-branch.c
+++ b/builtin-show-branch.c
@@@ -692,11 -701,11 +700,11 @@@ int cmd_show_branch(int ac, const char 
  
        /* If nothing is specified, try the default first */
        if (ac == 1 && default_num) {
-               ac = default_num + 1;
-               av = default_arg - 1; /* ick; we would not address av[0] */
+               ac = default_num;
+               av = default_arg;
        }
  
 -      ac = parse_options(ac, av, builtin_show_branch_options,
 +      ac = parse_options(ac, av, prefix, builtin_show_branch_options,
                           show_branch_usage, PARSE_OPT_STOP_AT_NON_OPTION);
        if (all_heads)
                all_remotes = 1;