Fixed build warnings on MSVC14 x64 in sweep context sources.

contrib/poly2tri/poly2tri/sweep/sweep_context.cc

@@ -96,7 +96,7 @@ void SweepContext::InitTriangulation()
 
 void SweepContext::InitEdges(std::vector<Point*> polyline)
 {
-  int num_points = polyline.size();
+  int num_points = static_cast<int>(polyline.size());
   for (int i = 0; i < num_points; i++) {
     int j = i < num_points - 1 ? i + 1 : 0;
     edge_list.push_back(new Edge(*polyline[i], *polyline[j]));

contrib/poly2tri/poly2tri/sweep/sweep_context.h

@@ -158,7 +158,7 @@ inline AdvancingFront* SweepContext::front()
 
 inline int SweepContext::point_count()
 {
-  return points_.size();
+  return static_cast<int>(points_.size());
 }
 
 inline void SweepContext::set_head(Point* p1)