Fix template preview sending invalid view requests

public.go

@@ -255,9 +255,14 @@ func handleRegisterCampaignView(c echo.Context) error {
 		campUUID = c.Param("campUUID")
 		subUUID  = c.Param("subUUID")
 	)
-	if _, err := app.queries.RegisterCampaignView.Exec(campUUID, subUUID); err != nil {
-		app.log.Printf("error registering campaign view: %s", err)
+
+	// Exclude dummy hits from template previews.
+	if campUUID != dummyUUID && subUUID != dummyUUID {
+		if _, err := app.queries.RegisterCampaignView.Exec(campUUID, subUUID); err != nil {
+			app.log.Printf("error registering campaign view: %s", err)
+		}
 	}
+
 	c.Response().Header().Set("Cache-Control", "no-cache")
 	return c.Blob(http.StatusOK, "image/png", pixelPNG)
 }

subscribers.go

@@ -17,6 +17,10 @@ import (
 	"github.com/lib/pq"
 )
 
+const (
+	dummyUUID = "00000000-0000-0000-0000-000000000000"
+)
+
 // subQueryReq is a "catch all" struct for reading various
 // subscriber related requests.
 type subQueryReq struct {
@@ -57,7 +61,7 @@ type subOptin struct {
 var dummySubscriber = models.Subscriber{
 	Email: "dummy@listmonk.app",
 	Name:  "Dummy Subscriber",
-	UUID:  "00000000-0000-0000-0000-000000000000",
+	UUID:  dummyUUID,
 }
 
 // handleGetSubscriber handles the retrieval of a single subscriber by ID.

templates.go

@@ -100,7 +100,7 @@ func handlePreviewTemplate(c echo.Context) error {
 
 	// Compile the template.
 	camp := models.Campaign{
-		UUID:         "00000000-0000-0000-0000-000000000000",
+		UUID:         dummyUUID,
 		Name:         "Dummy Campaign",
 		Subject:      "Dummy Campaign Subject",
 		FromEmail:    "dummy-campaign@listmonk.app",