[Fix] Fix add_datasample draw label bug

[Aierhaimian]

Motivation

I used demo.py to experience mmaction2, and set it to save the inference results. However, when I opened the result file to play, I found that the code did not correctly insert the inference label information into the video frame.

Modification

I found some bugs in the add_datasample method code of the ActionVisualizer class in lines 217-247 and made corresponding modifications.

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