Simplify and fix --save-period epoch 0 (#8042)

Simplify and update `--save-period` epoch 0

Author: glenn-jocher

train.py

@@ -423,7 +423,7 @@ def train(hyp, opt, device, callbacks):  # hyp is path/to/hyp.yaml or hyp dictio
                 torch.save(ckpt, last)
                 if best_fitness == fi:
                     torch.save(ckpt, best)
-                if (epoch > 0) and (opt.save_period > 0) and (epoch % opt.save_period == 0):
+                if opt.save_period > 0 and epoch % opt.save_period == 0:
                     torch.save(ckpt, w / f'epoch{epoch}.pt')
                 del ckpt
                 callbacks.run('on_model_save', last, epoch, final_epoch, best_fitness, fi)