Shotcut crashes previewing Stabilize filter when "preview scaling" is on

[Willian_Cruz]

With the new preview scaling on (thank you for it anyway, a very good idea), when Shotcut tries to play, or even show a still frame, of a clip that is using the Stabilize filter, it closes without warning or error message.

I’m using version 20.02.17.

Last lines of log just before the crash:

[Info   ] <MainWindow::showStatusMessage> "Saved D:\\Dropbox\\Fotos\\vadebike.org\\videos\\2020\\Ciclocomitê Paulista\\2020-03-16 Eleicao Ciclocomite Paulista\\eleicao ciclocomite paulista.mlt" 
[Debug  ] <Mlt::Controller::saveXML> writing temporary XML file "D:/Dropbox/Fotos/vadebike.org/videos/2020/Ciclocomitê Paulista/2020-03-16 Eleicao Ciclocomite Paulista/shotcut-y27184.mlt" 
[Debug  ] <Mlt::Controller::saveXML> copy to backup "D:\\Dropbox\\Fotos\\vadebike.org\\videos\\2020\\Ciclocomitê Paulista\\2020-03-16 Eleicao Ciclocomite Paulista\\eleicao ciclocomite paulista.mlt" "D:/Dropbox/Fotos/vadebike.org/videos/2020/Ciclocomitê Paulista/2020-03-16 Eleicao Ciclocomite Paulista/eleicao ciclocomite paulista - backup - A27184.mlt" 
[Debug  ] <Mlt::Controller::saveXML> rename "D:/Dropbox/Fotos/vadebike.org/videos/2020/Ciclocomitê Paulista/2020-03-16 Eleicao Ciclocomite Paulista/shotcut-y27184.mlt" "D:\\Dropbox\\Fotos\\vadebike.org\\videos\\2020\\Ciclocomitê Paulista\\2020-03-16 Eleicao Ciclocomite Paulista\\eleicao ciclocomite paulista.mlt" 
[Info   ] <MainWindow::showStatusMessage> "Saved D:\\Dropbox\\Fotos\\vadebike.org\\videos\\2020\\Ciclocomitê Paulista\\2020-03-16 Eleicao Ciclocomite Paulista\\eleicao ciclocomite paulista.mlt" 
[Debug  ] <MLT> [producer avformat] audio: total_streams 1 max_stream 1 total_channels 2 max_channels 2
[Info   ] <MLT> [filter dynamic_loudness] Reset. Old Pos: 4538	New Pos: 4023
[Debug  ] <MLT> [mlt_producer avformat-novalidate] "D:/Dropbox/Fotos/vadebike.org/videos/2020/Ciclocomitê Paulista/2020-03-16 Eleicao Ciclocomite Paulista/GX010200.MP4" checking VFR: pkt.duration %I64d
[Info   ] <MLT> [filter vidstab] Load results from D:/Dropbox/Fotos/vadebike.org/videos/2020/Ciclocomitê Paulista/2020-03-16 Eleicao Ciclocomite Paulista/stab2.stab
[Info   ] <MLT> [filter vidstab] Successfully loaded 113 motions

[shotcut]

I have only been able to reproduce when the clip is part of a multitrack where it must be composited or blended, which was already reported and fixed for some other filters. I just tested that the fix does apply to Stabilize as well. Consider it fixed for the next version.