Fix SIOOBe when extracting a resource without a path with usePath set to true

Fixes issue 1564


git-svn-id: http://svn.dmdirc.com/trunk@4453 00569f92-eb28-0410-84fd-f71c24880f

src/com/dmdirc/util/resourcemanager/ResourceManager.java

         
         File newDir;
         
-        if (usePath) {
+        if (usePath && resourceName.indexOf('/') > -1) {
             newDir = new File(directory,
                     resourceName.substring(0, resourceName.lastIndexOf('/')) + "/");
         } else {