[Fix] better deal with empty struct (must have shape [0])

Author: balbasty

mpython/core/base_types.py

@@ -51,7 +51,7 @@ def from_any(cls, other, **kwargs):
                     return None
 
                 elif type__ == "emptystruct":
-                    return Struct([])
+                    return Struct.from_shape([0])
 
                 elif type__ == "structarray":
                     # MPython returns a list of dictionaries in data__

mpython/struct.py

@@ -115,6 +115,9 @@ def _as_runtime(self) -> dict:
             data = MatlabType._to_runtime(data)
             return data
 
+        if np.ndarray.view(self, np.ndarray).size == 0:
+            return dict(type__="emptystruct")
+
         size = np.array([[*np.shape(self)]])
         data = np.ndarray.view(self, np.ndarray)
         data = np.reshape(data, [-1], order="F")