Fix #16 clear labels not working

models/issue.go

@@ -311,8 +311,8 @@ func (issue *Issue) clearLabels(e *xorm.Session) (err error) {
 		return fmt.Errorf("getLabels: %v", err)
 	}
 
-	for i := range issue.Labels {
-		if err = issue.removeLabel(e, issue.Labels[i]); err != nil {
+	for len(issue.Labels) > 0 {
+		if err = issue.removeLabel(e, issue.Labels[0]); err != nil {
 			return fmt.Errorf("removeLabel: %v", err)
 		}
 	}