王正一

Results 2 issues of 王正一

If user use `new Delete().from(StudentDAO.class).where("age = 100").executeSingle()` and the student is not exist, this may cause NullPointerException. I create this PR for this problem. link:https://github.com/pardom/ActiveAndroid/pull/510

Fix NullPointerException when user use delete with executeSingle Signed-off-by: wangzhengyi