[Fix] #448 Clamp 3D votes projections to image boundaries

[Divadi]

Fix issue #448:

• Projection of 3D seed points to image sometimes results in out-of-range image indices (by 1 or 2 pixels)
• Clamp the image indices to be within bounds

[CLAassistant]

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[yezhen17]

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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@b035bc8). Click here to learn what that means.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master     #463   +/-   ##
=========================================
  Coverage          ?   51.05%           
=========================================
  Files             ?      187           
  Lines             ?    13799           
  Branches          ?     2238           
=========================================
  Hits              ?     7045           
  Misses            ?     6277           
  Partials          ?      477           

Flag	Coverage Δ
unittests	51.05% <100.00%> (?)

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Impacted Files	Coverage Δ
mmdet3d/models/fusion_layers/vote_fusion.py	93.33% <100.00%> (ø)

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