`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, 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.