Handling unsupported SVG pattern elements

[combinatorial]

As far as I can tell SVG patterns are not supported. In the case that a drawing uses a pattern as a fill for example then the load fails, as there is an error.

I think it would be better if the import process reported there was an error. But still loaded the file, as in this example if the error is ignored you get the rect with a red fill (the fallback in resolvePainter)

e.g.