Merge branch 'jc/for-each-ref-head-segfault-fix'

Using a %(HEAD) placeholder in "for-each-ref --format=" option
caused the command to segfault when on an unborn branch.

* jc/for-each-ref-head-segfault-fix:
for-each-ref: do not segv with %(HEAD) on an unborn branch

diff --combined ref-filter.c
index d4c2931f3aab14accaa5720c87b2fc58aed83faa,d7e91a78da17e46d013a2b80895204d14604bd0e..f5f7a70c6d9b8ef36ecfe282167714640cace6b1
--- 1/ref-filter.c
--- 2/ref-filter.c
+++ b/ref-filter.c
@@@ -235,7 -235,7 +235,7 @@@ int parse_ref_filter_atom(const char *a
  {
        const char *sp;
        const char *arg;
 -      int i, at;
 +      int i, at, atom_len;
  
        sp = atom;
        if (*sp == '*' && sp < ep)
@@@ -250,19 -250,19 +250,19 @@@
                        return i;
        }
  
 +      /*
 +       * If the atom name has a colon, strip it and everything after
 +       * it off - it specifies the format for this entry, and
 +       * shouldn't be used for checking against the valid_atom
 +       * table.
 +       */
 +      arg = memchr(sp, ':', ep - sp);
 +      atom_len = (arg ? arg : ep) - sp;
 +
        /* Is the atom a valid one? */
        for (i = 0; i < ARRAY_SIZE(valid_atom); i++) {
                int len = strlen(valid_atom[i].name);
 -
 -              /*
 -               * If the atom name has a colon, strip it and everything after
 -               * it off - it specifies the format for this entry, and
 -               * shouldn't be used for checking against the valid_atom
 -               * table.
 -               */
 -              arg = memchr(sp, ':', ep - sp);
 -              if (len == (arg ? arg : ep) - sp &&
 -                  !memcmp(valid_atom[i].name, sp, len))
 +              if (len == atom_len && !memcmp(valid_atom[i].name, sp, len))
                        break;
        }
  
@@@ -1017,7 -1017,7 +1017,7 @@@ static void populate_value(struct ref_a
  
                        head = resolve_ref_unsafe("HEAD", RESOLVE_REF_READING,
                                                  sha1, NULL);
-                       if (!strcmp(ref->refname, head))
+                       if (head && !strcmp(ref->refname, head))
                                v->s = "*";
                        else
                                v->s = " ";
@@@ -1573,7 -1573,25 +1573,7 @@@ static int compare_refs(const void *a_
  void ref_array_sort(struct ref_sorting *sorting, struct ref_array *array)
  {
        ref_sorting = sorting;
 -      qsort(array->items, array->nr, sizeof(struct ref_array_item *), compare_refs);
 -}
 -
 -static int hex1(char ch)
 -{
 -      if ('0' <= ch && ch <= '9')
 -              return ch - '0';
 -      else if ('a' <= ch && ch <= 'f')
 -              return ch - 'a' + 10;
 -      else if ('A' <= ch && ch <= 'F')
 -              return ch - 'A' + 10;
 -      return -1;
 -}
 -static int hex2(const char *cp)
 -{
 -      if (cp[0] && cp[1])
 -              return (hex1(cp[0]) << 4) | hex1(cp[1]);
 -      else
 -              return -1;
 +      QSORT(array->items, array->nr, compare_refs);
  }
  
  static void append_literal(const char *cp, const char *ep, struct ref_formatting_state *state)
@@@ -1585,7 -1603,7 +1585,7 @@@
                        if (cp[1] == '%')
                                cp++;
                        else {
 -                              int ch = hex2(cp + 1);
 +                              int ch = hex2chr(cp + 1);
                                if (0 <= ch) {
                                        strbuf_addch(s, ch);
                                        cp += 3;