fix for multiple bugs in evolve operation mentioned in issue 1611

[nahidalam]

Currently there are multiple bugs in --evolve operation in the yolov7 repository.

• Bug 1: Evolve operation fails if there is zero weight in yolov7/train.py, line 674

x = x[random.choices(range(n), weights=w)[0]] # weighted selection

Solution of this bug is implemented here ultralytics/yolov5@e095b74

• Bug 2: Even if the bug 1 above is solved, users encountered below issue in yolov7/train.py line 688

hyp[k] = float(x[i + 7] * v[i])  # mutate
IndexError: index 30 is out of bounds for axis 0 with size 30

This is because the meta dictionary is not including the loss_ota parameter which is a new hyperparameter in yolov7.

Both the bugs are reported by multiple users in the issue here #1611

This PR resolves both of those bugs.

[shossain]

ship it!

[lnhutnam]

Tks u. It's very helpful :D