Fix refine_edges() Corner Ordering (AprilRobotics#188)

* fix issue with refine_edges reordering the apriltag corners, causing failures in the fallback case

apriltag.c

@@ -864,9 +864,10 @@ static void refine_edges(apriltag_detector_t *td, image_u8_t *im_orig, struct qu
 
  double L0 = W00*B0 + W01*B1;
 
- // compute intersection
- quad->p[i][0] = lines[i][0] + L0*A00;
- quad->p[i][1] = lines[i][1] + L0*A10;
+ // Compute intersection. Note that line i represents the line from corner i to (i+1)&3, so
+ // the intersection of line i with line (i+1)&3 represents corner (i+1)&3.
+ quad->p[(i+1)&3][0] = lines[i][0] + L0*A00;
+ quad->p[(i+1)&3][1] = lines[i][1] + L0*A10;
  } else {
  // this is a bad sign. We'll just keep the corner we had.
 // printf("bad det: %15f %15f %15f %15f %15f\n", A00, A11, A10, A01, det);