Don't crash on empty notify channel

........

Merged revisions 342715 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@342716 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_calendar.c

@@ -694,7 +694,7 @@ static void *do_notify(void *data)
 {
 	struct ast_calendar_event *event = data;
 	struct ast_dial *dial = NULL;
-	struct ast_str *apptext = NULL, *tmpstr;
+	struct ast_str *apptext = NULL, *tmpstr = NULL;
 	struct ast_datastore *datastore;
 	enum ast_dial_result res;
 	struct ast_channel *chan = NULL;