MKVToolNix 31.0.0 (32-bit)

What's new in this version:

New features and enhancements:
- all programs: added a new option `--abort-on-warnings` that will cause the program to abort after it has emitted the first warning, similar to how it aborts after the first error
- mkvmerge, mkvextract: when closing files that were opened for writing, cached data will not be flushed to storage automatically anymore. This reverts the workaround implemented for #2469. A new option was added to both programs (`--flush-on-close`) that re-enables flushing for people who are affected by data loss such as described in #2469.
- The reason is that automatic flushing causes long delays in processing queues when the output by mkvmerge/mkvextract isn't the final product but just an intermediate result to be processed further
- MKVToolNix GUI: multiplexer: the dialog previewing different character sets for text subtitles will now keep the position of the displayed text when switching between character sets

Bug fixes:
- mkvmerge: AVI reader: using DV type 1 AVIs will now result in an unsupported file type being reported (as the underlying AVI library doesn't support them) instead of crashing mkvmerge
- mkvmerge: HEVC: the height of interlaced streams will now be set correctly to the height of the full frame instead of the height of a single interlaced field
- mkvmerge: MP4 reader: edit lists consisting solely of elements that mkvmerge doesn't support (such as dwells) are simply ignored. Before no data was read for such tracks at all
- mkvmerge: text subtitles: entries with an explicit duration of 0ms will now be handled correctly: the 0ms duration will be stored in Matroska instead of the difference between the current and the following entry
- MKVToolNix GUI: multiplexer, chapter editor: fixed drag & drop handling with Qt 5.12.0 and newer
- MKVToolNix GUI: multiplexer: the GUI did not clean up temporary files created when running `mkvmerge`

Build system changes:
- Qt 5.4.0 or newer has required (up from 5.3.0) since version 30.0.0; I just forgot to include this entry