made more robust. See...

made more robust. See http://www.nabble.com/How-to-reference-library-JARs-of-a-plugin-at-runtime-%28URL%29-td15601148.html#a15601148


git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@7619 71c3de6d-444a-0410-be80-ed276b4c234a

remoting/src/main/java/hudson/remoting/Which.java

@@ -36,6 +36,7 @@ public class Which {
             int n = clazz.getName().split("\\.").length; // how many slashes do wo need to cut?
             for( ; n>0; n-- ) {
                 int idx = Math.max(resURL.lastIndexOf('/'), resURL.lastIndexOf('\\'));
+                if(idx<0)   throw new IllegalArgumentException(resURL);
                 resURL = resURL.substring(0,idx);
             }