fix unsqueeze

python/jittor/__init__.py

@@ -273,6 +273,7 @@ Var.start_grad = Var.detach_inplace = detach_inplace
 
 def unsqueeze(x, dim):
     shape = list(x.shape)
+    if dim < 0: dim += len(shape)
     assert dim <= len(shape)
     return x.reshape(shape[:dim] + [1] + shape[dim:])
 Var.unsqueeze = unsqueeze