.fuse() additional error checking

models/yolo.py

@@ -160,7 +160,7 @@ class Model(nn.Module):
     def fuse(self):  # fuse model Conv2d() + BatchNorm2d() layers
         print('Fusing layers... ')
         for m in self.model.modules():
-            if type(m) is Conv:
+            if type(m) is Conv and hasattr(Conv, 'bn'):
                 m._non_persistent_buffers_set = set()  # pytorch 1.6.0 compatability
                 m.conv = fuse_conv_and_bn(m.conv, m.bn)  # update conv
                 delattr(m, 'bn')  # remove batchnorm