Test for existence before trying to delete (thanks sebb)

git-svn-id: https://svn.apache.org/repos/asf/jmeter/trunk@1520921 13f79535-47bb-0310-9956-ffa450edef68
Test for existence before trying to delete (thanks sebb)

git-svn-id: https://svn.apache.org/repos/asf/jmeter/trunk@1520922 13f79535-47bb-0310-9956-ffa450edef68