[Fix] fix analyze log script

[xiexinch]

Thanks for your contribution and we appreciate it a lot. The following instructions would make your pull request more healthy and more easily get feedback. If you do not understand some items, don't worry, just make the pull request and seek help from maintainers.

Motivation

In some log files, iterations number is not correct, that may cause drawing unnecessary lines at log graph.

Modification

Add pre_iter to record pre-inters number at for loop.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMDet3D.
4. The documentation has been modified accordingly, like docstring or example tutorials.

#715

[codecov]

Codecov Report

Merging #716 (3c2bb13) into master (4d34581) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #716   +/-   ##
=======================================
  Coverage   85.28%   85.28%           
=======================================
  Files         107      107           
  Lines        5817     5817           
  Branches      952      952           
=======================================
  Hits         4961     4961           
  Misses        673      673           
  Partials      183      183           

Flag	Coverage Δ
unittests	85.26% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4d34581...3c2bb13. Read the comment docs.