`parse_style_attrs()` should not ignore errors
This code in parse_style_attrs
deliberately ignores parsing errors in attributes. Instead, it should call Node.set_error()
as in the rest of the code; this will cause the node not to be rendered.
The code ignores errors right now because of #261 (closed), where our parser for enable-background
is incorrect, and so we would mark the toplevel <svg>
element as being in error. By ignoring the error, we are at least able to render the test files in question.