identity: fix use-after-free in --usermap/--groupmap parse error path

identity_parse_map freed the str_dup'd list before logging the offending rule
( points into that buffer), causing an invalid read caught by CI valgrind
(MSAN/MSAN-style; the ONLY definite valgrind error in the suite).  Log before
freeing.  valgrind now reports 0 errors / 0 definite leaks in both the parent
and the forked wire-roundtrip child.

src/shared/identity.c

@@ -191,8 +191,9 @@ int identity_parse_map(Config* config, const char* value, bool is_group) {
   for (char* rule = strtok_r(list, ",", &saveptr); rule; rule = strtok_r(NULL, ",", &saveptr)) {
     char* colon = strchr(rule, ':');
     if (!colon || colon == rule) {
-      free(list);
+      /* Log before freeing: `rule` points into the str_dup'd list. */
       log_message(LOG_LEVEL_ERROR, "%s rules must be FROM:TO (got '%s')", optname, rule);
+      free(list);
       return -1;
     }
     *colon = '\0';