imapc: If mailbox select fails, rollback any changes done to it

Required by the following changes that start adding changes immediately
after SELECT. If the initial syncing doesn't finish successfully, these
changes need to be reverted.

src/lib-storage/index/imapc/imapc-mailbox.c

@@ -100,7 +100,12 @@ int imapc_mailbox_commit_delayed_trans(struct imapc_mailbox *mbox,
 
 	if (mbox->delayed_sync_view != NULL)
 		mail_index_view_close(&mbox->delayed_sync_view);
-	if (mbox->delayed_sync_trans != NULL) {
+	if (mbox->delayed_sync_trans == NULL)
+		;
+	else if (!mbox->selected) {
+		/* ignore any changes done during SELECT */
+		mail_index_transaction_rollback(&mbox->delayed_sync_trans);
+	} else {
 		if (mail_index_transaction_commit(&mbox->delayed_sync_trans) < 0) {
 			mailbox_set_index_error(&mbox->box);
 			ret = -1;