when drawImage a empty C2S context
when drawImage a empty C2S context

Null pointer error will be thrown when ctx.drawImage(ctx) with an empty C2S context with no childNodes.

These code may fix the problem.
zenozeng/svgcanvas,zenozeng/canvas2svg,gliffy/canvas2svg,zenozeng/svgcanvas,zenozeng/canvas2svg,gliffy/canvas2svg