Select an audio track defaults to installation folder

[whoisrich]

First, thanks for making such an excellent program

Just want to mention one thing I kept noticing when doing some editing:

- When you open or append a video file, it defaults to your last used folder.
- BUT when selecting to add an audio track, it defaults to the installation folder.

So this means you keep having to navigate to your working folder when making audio changes.

Avidemux 2.6.6 on Windows.