fix reverse of empty linestrings (#163)

Signed-off-by: Jochen.Mehlhorn <jochen.mehlhorn@mercedes-benz.com>

Author: jo-me

line_string.go

@@ -17,6 +17,11 @@ func (ls LineString) Dimensions() int {
 // This is done inplace, ie. it modifies the original data.
 func (ls LineString) Reverse() {
 	l := len(ls) - 1
+
+	if l < 1 {
+		return
+	}
+
 	for i := 0; i <= l/2; i++ {
 		ls[i], ls[l-i] = ls[l-i], ls[i]
 	}

line_string_test.go

@@ -20,6 +20,16 @@ func TestLineStringReverse(t *testing.T) {
 		input  LineString
 		output LineString
 	}{
+		{
+			name:   "0 point line",
+			input:  LineString{},
+			output: LineString{},
+		},
+		{
+			name:   "1 point line",
+			input:  LineString{{1, 2}},
+			output: LineString{{1, 2}},
+		},
 		{
 			name:   "2 point line",
 			input:  LineString{{1, 2}, {3, 4}},