fix crash on export per command line with sample track

[BaraMGB]

this should fix #3338

@zonkmachine can you look at this?

[zonkmachine]

Now the file loads and exports fine but never hands back to main() . The Render Manger is stuck reporting 100% .

[zonkmachine]

Sometimes it renders just fine. I think I've seen this before. Just once in a while a render will fail to complete. It may be that you've poked another bug a bit. I'll continue testing this to see if I can find a pattern in it.

[BaraMGB]

Does it depends on the project?

[zonkmachine]

Does it depends on the project?

It seem to depend on the length of the samples. I'm testing this with noise samples of various length and with a 15 second sample in the project there is about 50% chance of the renderer getting stuck after export.

[zonkmachine]

Sorry. I went back 50 commits and this bug is there also. It's hard to see a real pattern in it though other than the sample track being involved. This commit fixes the issue reported and should be merged. I can probe into the hanging renderer a bit more and write a new issue for it.

[zonkmachine]

The hanging render on longer Sample Tracks is an SDL thing.
I'm not done bisecting this but it may have happened around these commits 8497d39 e55ec80

[zonkmachine]

New issue opened for the SDL issues here: #3344
I suggest you merge this.

[BaraMGB]

Okay. Thanks for the investigation