AnalyserModel: scoping issue

[hsorby]

When trying to generate some code for a model that used imports the generation of the implementation code fails if the analysed model is not in scope. This appears different from when the model does no use imports.

[hsorby]

The issue wasn't around the use of imports but how units with child units are determined. Losing the model that the units are defined on made it impossible to determine compatibility. This lead to a division by zero when calculating the scale factor for units in the code generation.