change video reader to 0-based indexing

[ycxioooong]

No description provided.

[codecov]

Codecov Report

Merging #8 into master will decrease coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master       #8      +/-   ##
==========================================
- Coverage   53.37%   53.35%   -0.03%     
==========================================
  Files          53       53              
  Lines        1911     1910       -1     
==========================================
- Hits         1020     1019       -1     
  Misses        891      891

Impacted Files	Coverage Δ
mmcv/video/io.py	95.56% <100%> (-0.03%)	⬇️

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[OpenMMLab-Assistant-007]

Hi!
@ycxioooong
First of all, we want to express our gratitude for your significant PR in the OpenMMLab project. Your contribution is highly appreciated, and we are grateful for your efforts in helping improve this open-source project during your personal time. We believe that many developers will benefit from your PR.

We would also like to invite you to join our Special Interest Group (SIG) private channel on Discord, where you can share your experiences, ideas, and build connections with like-minded peers. To join the SIG channel, simply message moderator— OpenMMLab on Discord or briefly share your open-source contributions in the #introductions channel and we will assist you. Look forward to seeing you there! Join us ：https://discord.gg/UjgXkPWNqA

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