Noticed that sometimes a tooltip tries to get triggered on a non-existent row
in the VFS File browser.  So, protect against that by checking the result of
tableView.getRowAt(y) to see if there is a row there before using the value
to index into the table data.


git-svn-id: https://svn.apache.org/repos/asf/pivot/trunk@1587271 13f79535-47bb-0310-9956-ffa450edef68