Fix some small issues that were flagged by upcoming lint checks. (golang#138)

Author: rsned

s2/cell_test.go

@@ -750,8 +750,6 @@ func TestCellDistanceToEdge(t *testing.T) {
 			expectedError = 3e-8
 		} else if expectedMin.Radians() <= math.Pi/3 {
 			expectedError = 1e-15
-		} else {
-			expectedError = 1e-12
 		}
 
 		if !float64Near(expectedMin.Radians(), actualMin.Radians(), expectedError) {

s2/edge_distances.go

@@ -336,7 +336,6 @@ func updateEdgePairMinDistance(a0, a1, b0, b1 Point, minDist s1.ChordAngle) (s1.
 		return 0, false
 	}
 	if CrossingSign(a0, a1, b0, b1) == Cross {
-		minDist = 0
 		return 0, true
 	}
 

s2/point.go

@@ -344,7 +344,7 @@ func (p Point) IsNormalizable() bool {
 func (p Point) EnsureNormalizable() Point {
 	// TODO(rsned): Zero vector isn't normalizable, and we don't have DCHECK in Go.
 	// What is the appropriate return value in this case? Is it {NaN, NaN, NaN}?
-	if p == (Point{r3.Vector{0, 0, 0}}) {
+	if p == (Point{r3.Vector{X: 0, Y: 0, Z: 0}}) {
 		return p
 	}
 	if !p.IsNormalizable() {

s2/shapeindex.go

@@ -1466,9 +1466,11 @@ func (s *ShapeIndex) absorbIndexCell(p *PaddedCell, iter *ShapeIndexIterator, ed
 	}
 
 	// Update the edge list and delete this cell from the index.
-	edges, newEdges = newEdges, edges
+	// TODO(rsned): Figure out best fix for this. Linters are
+	// flagging the swap because newEdges is no longer used after
+	// this.
+	edges, newEdges = newEdges, edges // nolint
 	delete(s.cellMap, p.id)
-	// TODO(roberts): delete from s.Cells
 }
 
 // testAllEdges calls the trackers testEdge on all edges from shapes that have interiors.