[CSV-121] Exception that the header contains duplicate names when the column names are empty. Add a test that shows that ONE missing header is OK.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/csv/trunk@1602166 13f79535-47bb-0310-9956-ffa450edef68
[CSV-121] Exception that the header contains duplicate names when the column names are empty. Add a test that shows that TWO missing header is not OK.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/csv/trunk@1602168 13f79535-47bb-0310-9956-ffa450edef68