Creating archive in the working directory causes NullPointerException

The following will cause `NullPointerException`:
```java
archiver.setDestFile( new File( "archive.zip" ) );
```
That is because `setDestFile` tries to create the parent directory:
```java
        if ( destFile != null )
        {
            destFile.getParentFile().mkdirs();
        }
```
but in the case shown above `destFile.getParentFile()` returns `null`.