fix bugs in bottom-up keypoint score

[wusize]

Setting all joint scores to be 0 would cause erroneous results in testing for bottom-up approach

[codecov]

Codecov Report

Merging #548 (9caf8e5) into master (6ff9938) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

❗ Current head 9caf8e5 differs from pull request most recent head fdc4a2b. Consider uploading reports for the commit fdc4a2b to get more accurate results

@@            Coverage Diff             @@
##           master     #548      +/-   ##
==========================================
- Coverage   82.08%   82.03%   -0.05%     
==========================================
  Files         150      150              
  Lines       10199    10199              
  Branches     1623     1623              
==========================================
- Hits         8372     8367       -5     
- Misses       1450     1453       +3     
- Partials      377      379       +2     

Flag	Coverage Δ
unittests	81.95% <100.00%> (-0.03%)	⬇️

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Impacted Files	Coverage Δ
mmpose/core/post_processing/post_transforms.py	95.04% <100.00%> (ø)
mmpose/datasets/pipelines/shared_transform.py	83.52% <0.00%> (-2.95%)	⬇️

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[innerlee]

Adding a unittest for this error would be great

[innerlee]

And, does this change affect any scores in modelzoo?

[jin-s13]

This bug is caused by upgrading xtcocotools (in the newer version of xtcocotools, those keypoints with zero-score will be ignored.)

[innerlee]

Note for future readers: Please use mmpose >= v0.13.0 if you use xtcocotools >= 1.7