Fix minor leak in kadmind password change dispatch

In the unlikely event that kadmind cannot resolve the KDB keytab in
schpw.c:dispatch(), don't leak the error message.  Reported by Bean
Zhang.

src/kadmin/server/schpw.c

@@ -438,11 +438,14 @@ dispatch(void *handle, const krb5_fulladdr *local_addr,
     krb5_keytab kt = NULL;
     kadm5_server_handle_t server_handle = (kadm5_server_handle_t)handle;
     krb5_data *response = NULL;
+    const char *emsg;
 
     ret = krb5_kt_resolve(server_handle->context, "KDB:", &kt);
     if (ret != 0) {
+        emsg = krb5_get_error_message(server_handle->context, ret);
         krb5_klog_syslog(LOG_ERR, _("chpw: Couldn't open admin keytab %s"),
-                         krb5_get_error_message(server_handle->context, ret));
+                         emsg);
+        krb5_free_error_message(server_handle->context, emsg);
         goto egress;
     }