Bug 422101

SUMMARY
If you have a video clip with one or more guides and you create scripts to export the video from Start -> Guide 1 and Guide 1 - End the last video is missing several minutes at the end while the rendering was finished with no errors

Example:
Video duration: 00:51:07
Guide at: 00:25:31
First video Start -> 00:25:31
2nd Video: 00:25:31 -> End (00:51:07)
The first video has the correct duration while the 2nd video is only 17:15 long but should be 24:36 long.

STEPS TO REPRODUCE
1. Create Kdenlive project
2. Drop guides
3. Create export script which do export guide areas
4. Render the last video
5. Find several frames/minutes/seconds missing at the end.

OBSERVED RESULT
- Missing frames at the end

EXPECTED RESULT
- Correctly exproted video

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: openSUSE Tumbleweed 20200520 (Kernel: 5.6.12)
(available in About System)
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.70.0
Qt Version: 5.14.1