GetJREPath() JLI function fails to locate libjava.so if not standard Java launcher is used

I have put together an hello world application, with a jarfile. If I jpackage it with the following command line:

```
$ jpackage --type app-image --name HelloWorld --input out/artifacts/jpackage_test_jar --main-jar jpackage-test.jar --dest output
```

Everything works correctly, and launching the generated app prints "Hello world":

```
$ output/HelloWorld/bin/HelloWorld
Hello world!
```

However, if the destination directory contains "bin" (even as a nested subfolder), there are issues. Here's the jextract command line:

```
$ jpackage --type app-image --name HelloWorld --input out/artifacts/jpackage_test_jar --main-jar jpackage-test.jar --dest bin
```

(the only thihng that changed is the --dest parameter)

And here's what I get:

```
$ bin/HelloWorld/bin/HelloWorld
Error: could not find libjava.so
Error: Could not find Java SE Runtime Environment.
```

I use Ubuntu 20.04. A colleague of mine using MacOS does not seem to have the same issue, so it seems to be system specific.

I'm using the latest jpackage from jdk/jdk.

See:
https://mail.openjdk.java.net/pipermail/core-libs-dev/2021-June/079041.html