Make sure time is valid for uptime (bug 1214)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@2417 65c4cc65-6c06-0410-ace0-fbb531ad65f3

cli.c

@@ -186,6 +186,8 @@ static char *format_uptimestr(time_t timeval)
 #define WEEK (DAY*7)
 #define YEAR (DAY*365)
 
+	if (timeval < 0)
+		return NULL;
 	if (timeval > YEAR) {
 		years = (timeval / YEAR);
 		timeval -= (years * YEAR);