When putting some wrong parameters (hevc with avc options), my command-line stalled:

```
gpac -i avgen:dur=2  @ enc:gfloc:c=hevc:b=5100k:r=30/1:bf=2:b_strategy=0:fintra=2:profile=high:color_primaries=1:color_trc=1:colorspace=1::x264-params="level=40:no-open-gop=1:scenecut=0" -o hevc.mp4
```
command-line never exits
This is a GitHub Issue
repo:gpac
owner:gpac
Title : command-line never exits
Issue date:

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When putting some wrong parameters (hevc with avc options), my command-line stalled:

```
gpac -i avgen:dur=2  @ enc:gfloc:c=hevc:b=5100k:r=30/1:bf=2:b_strategy=0:fintra=2:profile=high:color_primaries=1:color_trc=1:colorspace=1::x264-params="level=40:no-open-gop=1:scenecut=0" -o hevc.mp4
```
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