utils.load_weights doesn't work for custom number of classes

[dinesh-tadi]

Loading yolov4.weights for 80 classes works fine but I wanted to use yolov4.conv.137 for the custom number of classes (as this is available in the official darknet repo for training for the custom number of classes, I read that this weights file contains the weights for the layers except for the Yolo layer), but it doesn't work and gives all outputs as nan. Any suggestions on how to modify the utils.load_weights function so that I can load this file?

[ahoereth]

Related: #180 & #181