Resolve "OpenCV grabber loop mode & duration"

What does this MR do?

Correct the duration calculation. Use total number of frame and current frame index to loop the video.

How to test it?

• Use OpenCV grabber to read a video
• Check the duration (using videoQt::editor::SSlider)
• Check the loop mode

Additional tests to run

• windows
• macos
• linux

• Video format:

• MP4
• AVI
• Others

Associated Issues/Merge Requests

• Issues
  • Closes #252 (closed)