[evolution-data-server] Bug 791016 - [Camel] Fix a compiler warning at folder_summary_update_counts_by_flags()

[Milan Crha <mcrha src gnome org>]

commit 879be784ab361e952f3011a5ff0c807fcccf537a
Author: Philip Withnall <withnall endlessm com>
Date:   Fri Dec 1 09:48:55 2017 +0100

    Bug 791016 - [Camel] Fix a compiler warning at folder_summary_update_counts_by_flags()

 src/camel/camel-folder-summary.c |    6 ++----
 1 files changed, 2 insertions(+), 4 deletions(-)
---
diff --git a/src/camel/camel-folder-summary.c b/src/camel/camel-folder-summary.c
index f966e8e..dfca052 100644
--- a/src/camel/camel-folder-summary.c
+++ b/src/camel/camel-folder-summary.c
@@ -427,10 +427,8 @@ folder_summary_update_counts_by_flags (CamelFolderSummary *summary,
                unread = 0;
 
        if (unread) {
-               summary->priv->unread_count += unread;
-
-               if (summary->priv->unread_count < 0)
-                       summary->priv->unread_count = 0;
+               if (unread > 0 || summary->priv->unread_count)
+                       summary->priv->unread_count += unread;
 
                g_object_notify (summary_object, "unread-count");
                changed = TRUE;