validate that TimeInMeshQuantum is non-zero

otherwise we get a division by zero

score_params.go

@@ -179,6 +179,9 @@ func (p *TopicScoreParams) validate() error {
 	}
 
 	// check P1
+	if p.TimeInMeshQuantum == 0 {
+		return fmt.Errorf("invalid TimeInMeshQuantum; must be non zero")
+	}
 	if p.TimeInMeshWeight < 0 {
 		return fmt.Errorf("invalid TimeInMeshWeight; must be positive (or 0 to disable)")
 	}

score_params_test.go

@@ -32,6 +32,10 @@ func TestPeerScoreThresholdsValidation(t *testing.T) {
 }
 
 func TestTopicScoreParamsValidation(t *testing.T) {
+	if (&TopicScoreParams{}).validate() == nil {
+		t.Fatal("expected validation error")
+	}
+
 	if (&TopicScoreParams{TopicWeight: -1}).validate() == nil {
 		t.Fatal("expected validation error")
 	}