to avoid integer overflow during the polygon operations in make_brim(), plateoffset is applied during gcode generation. This results in a wrong first layer convexhull "m_first_layer_convex_hull" which is used in _make_skrit(). This patch fixs this issue. JIRA: https://jira.bambooolab.com/browse/STUDIO-3719 Change-Id: Icfe21f4dbab05cc9e1c6f668791a62f954c2e0e5 (cherry picked from commit 6286b3e447b7ac7cbc061dca435091094783f74b)