Fix add component bug where transform parent could not be found by index

nexus_constructor/qml_models/instrument_model.py

@@ -324,7 +324,17 @@ def update_child_transforms(self, component):
 
     @Slot(int, result="QVariant")
     def get_transform_model(self, index: int):
-        return self.transform_models[index]
+        """
+        Returns the transform model for the component.
+        The list is 1-based due to the 0 being no parent, so we have to use index-1 here
+        unless the component has no transform parent (for example the sample)
+        :param index: The component's transform parents index.
+        :return: The transform model for the component.
+        """
+        if index == 0:
+            return self.transform_models[index]
+        else:
+            return self.transform_models[index - 1]
 
     @Slot(str, result=str)
     def generate_component_name(self, base):