res_calendar: Protect channel when adding datastore.

This change adds a missing channel lock when adding a datastore
to a channel.
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Merged revisions 404135 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 404136 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 404137 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@404138 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_calendar.c

@@ -775,7 +775,10 @@ static void *do_notify(void *data)
 	datastore->inheritance = DATASTORE_INHERIT_FOREVER;
 
 	ao2_ref(event, +1);
+
+	ast_channel_lock(chan);
 	res = ast_channel_datastore_add(chan, datastore);
+	ast_channel_unlock(chan);
 
 	if (!(tmpstr = ast_str_create(32))) {
 		goto notify_cleanup;