Latest version seems to be ignoring the "ffmpegExt" config

[BinaryMan101]

Running on the latest version (20211104), the ffmpeg configuration seems to be ignoring the "ffmpegExt" variable. I use the following configurations to convert ugoira to mp4:

ffmpeg = ffmpeg
ffmpegCodec = libx264
ffmpegExt = mp4
ffmpegParam = -vsync 2 -r 999 -pix_fmt yuv420p -preset medium -crf 18 -tune animation -an -vf "pad=ceil(iw/2)*2:ceil(ih/2)*2"

But when it tries converting, it fails as follows:

2021-11-08 13:29:53,267 - PixivUtil20211104 - INFO - [convert_ugoira()] running with cmd: ffmpeg -y -safe 0 -i "C:/Users/the_o/AppData/Local/Temp/convert_ugoirajnpbw3ik/i.ffconcat" -c:v libx264 -vsync 2 -r 999 -pix_fmt yuv420p -preset medium -crf 18 -tune animation -an -vf "pad=ceil(iw/2)*2:ceil(ih/2)*2" "C:/Users/the_o/AppData/Local/Temp/convert_ugoirajnpbw3ik/temp.webm"
2021-11-08 13:29:53,273 - PixivUtil20211104 - INFO - Start encoding E:\Downloads\PixivDump\94007045_ugoira1920x1080.mp4
2021-11-08 13:29:53,343 - PixivUtil20211104 - ERROR - Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
2021-11-08 13:29:53,343 - PixivUtil20211104 - ERROR - NoneType: None

2021-11-08 13:29:53,351 - PixivUtil20211104 - ERROR - Failed when converting image using ffmpeg -y -safe 0 -i "C:/Users/the_o/AppData/Local/Temp/convert_ugoirajnpbw3ik/i.ffconcat" -c:v libx264 -vsync 2 -r 999 -pix_fmt yuv420p -preset medium -crf 18 -tune animation -an -vf "pad=ceil(iw/2)*2:ceil(ih/2)*2" "C:/Users/the_o/AppData/Local/Temp/convert_ugoirajnpbw3ik/temp.webm" ==> ffmpeg return exit code=1, expected to return 0.
2021-11-08 13:29:53,351 - PixivUtil20211104 - ERROR - NoneType: None

The destination file is correct, but ffmpeg is trying to output a "temp.webm" file, despite being configurated for "mp4".