use EMPTY_STRING in _parent_via_in_reply_to

This is a review suggestion [1] of Tomi. I decided not to squash it
so that the code movement remains clear.

[1]: id:m2pnxxgf5q.fsf@guru.guru-group.fi

diff --git a/lib/thread.cc b/lib/thread.cc
index 62dbd3b345482ccb901b8c05c135238f35bc0264..4711319d2cf67618edfe7c74b78a0c940bbf9784 100644 (file)
--- a/lib/thread.cc
+++ b/lib/thread.cc
@@ -402,7 +402,7 @@ _parent_via_in_reply_to (notmuch_thread_t *thread, notmuch_message_t *message) {
     THREAD_DEBUG("checking message = %s in_reply_to=%s\n",
                 notmuch_message_get_message_id (message), in_reply_to);
 
-    if (in_reply_to && strlen (in_reply_to) &&
+    if (in_reply_to && (! EMPTY_STRING(in_reply_to)) &&
        g_hash_table_lookup_extended (thread->message_hash,
                                      in_reply_to, NULL,
                                      (void **) &parent)) {