Fix T62883: Import SVG file remove fill color.

rBbc5b0f7a091c changed the default fill mode for curves.
Instead of being "fill" it is now "none".
The creates a problem because the svg importer seems to rely on curves being filled by default.

This diff should fix it.

(Note that this is my first patch)

Reviewers: sergey, mont29

Reviewed By: mont29

Subscribers: mont29

Differential Revision: https://developer.blender.org/D4582