Calculation AP in model_eval.py

[rongyixiao]

Hello,

view pairs with max OKSs as match ones, add to oks_all

oks_all = np.concatenate((oks_all, np.max(oks, axis=1)), axis=0)

accumulate total num by max(gtN,pN)

oks_num += np.max(oks.shape)

is there error about oks_num?