Ported fix of solid layer count from Ultimaker/CuraEngine#140
Ported fix of solid layer count from Ultimaker/CuraEngine#140

Fixes #1692

JackGavin13/octoprint-test-not-finished,foosel/OctoPrint,Jaesin/OctoPrint,beeverycreative/BEEweb,JackGavin13/octoprint-test-not-finished,foosel/OctoPrint,Jaesin/OctoPrint,JackGavin13/octoprint-test-not-finished,beeverycreative/BEEweb,beeverycreative/BEEweb,beeverycreative/BEEweb,foosel/OctoPrint,bicephale/OctoPrint,Salandora/OctoPrint,JackGavin13/octoprint-test-not-finished,bicephale/OctoPrint,foosel/OctoPrint,Salandora/OctoPrint,bicephale/OctoPrint,Jaesin/OctoPrint,bicephale/OctoPrint,Jaesin/OctoPrint,Salandora/OctoPrint,Salandora/OctoPrint