for JNLP file without codebase and href; and if the main jar is located in a sub directory, we will generate incorrect codebase.

e.g <jar href="jarsubdir/main.jar"/>

this is because for JNLP file without codebase and href, we need to get href to jnlp using the main jar. (canonical home: http://host.com/jarsubdir/main.jarjnlp)

current code simply deduce codebase from canonical home, so the codebase becomes:
http://host.com/jarsubdir

and then later we will try to fetch jar from: http://host.com/jarsubdir/jarsubdir/main.jar

which is not correct.