Fix possible image drawing issues (#13423)

* Update plots.py

Fixed non-meaningful labels in the top right (row 1, column 4) plots when batch size is larger than max_subplots.

Signed-off-by: zzzer <48149018+zhixuwei@users.noreply.github.com>

* Update plots.py

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

* Auto-format by https://ultralytics.com/actions

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Signed-off-by: zzzer <48149018+zhixuwei@users.noreply.github.com>
Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>
Co-authored-by: UltralyticsAssistant <web@ultralytics.com>