vectorize module passes undefined paths variable

To recreate:

• Get this PCB traces file: https://calischs.pages.cba.mit.edu/nrf52/bc832-ftdi/bc832-nrf-ftdi-traces.png
• Open SRM-20 PCB server program
• Input file and select "mill traces". Change offset number to 0 to fill.
• At some point the variable "sortpath" in vectorize will become undefined and the routine will halt. We get a "cannot read length of undefined" in console.
• Unchecking "sort distance" in the vectorize module eliminates the problem.

Seems like a bug. I haven't had time to investigate more thoroughly, but I just wanted to make a note of this.