Fix rare use of undefined variable

[starboerg]

Variable x2 was used undefined in case of polygons without y-extend. Defaulting x2 to zero works around this issue.

[codecov]

Codecov Report

Merging #196 (54d1d6d) into master (ee30f6e) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #196   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           36        36           
  Lines         1107      1108    +1     
=========================================
+ Hits          1107      1108    +1     

Impacted Files	Coverage Δ
src/svg.js	100.00% <100.00%> (ø)

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[magjac]

@starboerg Thanks for the contribution and apologies for the delay. Can you provide an example that trigger this? Or even better, add a test case?

[starboerg]

@magjac I did not dive too deep into the code, just stumbled upon this issue. I use a sequence of graphs and transition them into each other:
graphviz.transition(function () { return d3.transition("main").ease(d3.easeLinear).delay(0).duration(500); });
Likely a horizontal line element in the graphs triggers this, but I did not keep any example.