[Fix] Fix a potential overflow bug when post_max_size is set too large in the circle_nms (#1225)

* [Fix] overflow bug

* [Fix] typo
Co-authored-by: zeyuzeng <zeyuzeng@autox.ai>
Co-authored-by: zeyu-hello <zeyuzeng@hotmail.com>

mmdet3d/core/post_processing/box3d_nms.py

@@ -219,4 +219,8 @@ def circle_nms(dets, thresh, post_max_size=83):
             # ovr = inter / areas[j]
             if dist <= thresh:
                 suppressed[j] = 1
-    return keep[:post_max_size]
+
+    if post_max_size < len(keep):
+        return keep[:post_max_size]
+
+    return keep