fix a bug in svgToString function: some elements have no attribute, so when convert it to stinrg some namespace can't be set correctly.
fix a bug in svgToString function:
some elements have no attribute, so when convert it to stinrg some namespace can't be set correctly.

now, the tag like this can be correctly converted:
<se:mytag>hello</se:mytag>
kvasilov48/SVG-edit,korya/svg-edit,korya/svg-edit,kvasilov48/SVG-edit,korya/svg-edit,kvasilov48/SVG-edit,korya/svg-edit