[Core] get_tensor_datatype where initializers don't have ValueInfo

Author: maltanar

src/qonnx/core/modelwrapper.py

@@ -198,7 +198,11 @@ def get_tensor_datatype(self, tensor_name):
             # TensorProto.INT64 : "INT64",
         }
         tensor_vi = self.get_tensor_valueinfo(tensor_name)
-        onnx_dtype = tensor_vi.type.tensor_type.elem_type
+        if tensor_vi is None:
+            # some initialized tensors don't get ValueInfo even after shape inference
+            _, onnx_dtype = self.get_initializer(tensor_name, return_dtype=True)
+        else:
+            onnx_dtype = tensor_vi.type.tensor_type.elem_type
         if onnx_dtype in onnx_dtype_to_qonnx_dtype.keys():
             return DataType[onnx_dtype_to_qonnx_dtype[onnx_dtype]]
         else: