Use ascii file mode for vid.stab
Use ascii file mode for vid.stab

For accuracy value > 9, vid.stab creates a binary analysis file that
it can not read properly - causing memory exhaustion and crash.
Ascii file format does not have that problem.

Fixes:
https://forum.shotcut.org/t/please-test-the-version-21-06-release-candidate/28284/16

j-b-m/mlt,j-b-m/mlt,mltframework/mlt,mltframework/mlt,mltframework/mlt,mltframework/mlt,j-b-m/mlt,j-b-m/mlt,mltframework/mlt,mltframework/mlt,mltframework/mlt,j-b-m/mlt,mltframework/mlt,j-b-m/mlt,mltframework/mlt,mltframework/mlt,j-b-m/mlt,j-b-m/mlt,j-b-m/mlt,j-b-m/mlt