Bug on F1-score calculation

[splionar]

As pointed out in NU-MCC (https://github.com/sail-sg/numcc), there is a bug in MCC's F1-score calculation.

The bug is located in

MCC/engine_mcc.py

Line 44 in b04c975

for i in range(int(np.ceil(predicted_xyz.shape[0] / slice_size))):

predicted_xyz should be gt_xyz.

This bug hurts MCC metrics when the number of predicted points are less than ground truth points. After fixing this bug, higher F1-score can be obtained by setting higher --eval_score_threshold.