Avoid division by zero in the rare case that portsnap needs to fetch

zero patches.  (This avoids two "dc: divide by zero" warnings.)

MFC after:	3 days

usr.sbin/portsnap/portsnap/portsnap.sh

@@ -619,8 +619,10 @@ fetch_progress() {
 
 pct_fmt()
 {
-	printf "                                     \r"
-	printf "($1/$2) %02.2f%% " `echo "scale=4;$LNC / $TOTAL * 100"|bc`
+	if [ $TOTAL -gt 0 ]; then
+		printf "                                     \r"
+		printf "($1/$2) %02.2f%% " `echo "scale=4;$LNC / $TOTAL * 100"|bc`
+	fi
 }
 
 fetch_progress_percent() {