fix-null-exception

[EArminjon]

The following SVG throw an exception (when using flutter_svg) : https://sweden.a.bigcontent.io/v1/static/10000199.

This SVG contain an empty tag : <polygon xmlns="http://www.w3.org/2000/svg" fill="#0a287d" points="" id="polygon7"/> which lead to the issue.

Checking as this PR did if path is null avoid the issue.