Get BasicSampler(0), RandomSampler(0), and BurstSampler(0) to behave …

…the same and not write anything (#696)

sampler.go

@@ -47,6 +47,9 @@ type BasicSampler struct {
 // Sample implements the Sampler interface.
 func (s *BasicSampler) Sample(lvl Level) bool {
 	n := s.N
+	if n == 0 {
+		return false
+	}
 	if n == 1 {
 		return true
 	}

sampler_test.go

@@ -28,20 +28,41 @@ var samplers = []struct {
 		},
 		100, 20, 20,
 	},
+	{
+		"BasicSampler_0",
+		func() Sampler {
+			return &BasicSampler{N: 0}
+		},
+		100, 0, 0,
+	},
 	{
 		"RandomSampler",
 		func() Sampler {
 			return RandomSampler(5)
 		},
 		100, 10, 30,
 	},
+	{
+		"RandomSampler_0",
+		func() Sampler {
+			return RandomSampler(0)
+		},
+		100, 0, 0,
+	},
 	{
 		"BurstSampler",
 		func() Sampler {
 			return &BurstSampler{Burst: 20, Period: time.Second}
 		},
 		100, 20, 20,
 	},
+	{
+		"BurstSampler_0",
+		func() Sampler {
+			return &BurstSampler{Burst: 0, Period: time.Second}
+		},
+		100, 0, 0,
+	},
 	{
 		"BurstSamplerNext",
 		func() Sampler {