Fails if bias = False

[yukimasano]

Hi, I've noticed the export fails if a Layer has zero bias.

For others having this problem, this function sets the bias to zero.

def search_set_bias(model):
    for m in model.children():
        if isinstance(m,torch.nn.Linear) or isinstance(m, torch.nn.Conv2d):
            if m.bias is None:
                m.bias = torch.nn.Parameter(torch.zeros(m.weight.size(0)))
        search_set_bias(m)