Fix Visuliazer that built vis_backends will not be used when save_dir is None 修复 Visualizer 的 save_dir 参数为 None 时，传入构建好的 vis_backends 不起作用的问题

[OpenMMLab-Assistant-004]

Fix Visuliazer that built vis_backends will not be used when save_dir is None

修复 Visualizer 的 save_dir 参数为 None 时，传入构建好的 vis_backends 不起作用的问题

open-mmlab/mmengine#1267

open-mmlab/mmengine#1267

Task Information

Repository：MMEngine

Difficulty：Easy

Points：30

Estimated Time Consumption：14 days

Task Status

Claimant's Github ID：None

Claim Time：None

PR Link：None

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[Crescent-Saturn]

I think this task has already been completed by this PR: open-mmlab/mmengine#1275