Fix display tab "New page" on fresh project

Author: kubiix

Yafc.Model/Model/Project.cs

@@ -45,6 +45,16 @@ public override ModelObject? ownerObject {
         internal set => throw new NotSupportedException();
     }
 
+    public void AssureFirstPage() {
+        if (pages.Count == 0) {
+            ProjectPage firstPage = new ProjectPage(this, typeof(ProductionTable));
+            pages.Add(firstPage);
+            pagesByGuid[firstPage.guid] = firstPage;
+
+            displayPages.Add(firstPage.guid);
+        }
+    }
+
     private void UpdatePageMapping() {
         hiddenPages = 0;
         pagesByGuid.Clear();

Yafc/Windows/MainScreen.cs

@@ -79,15 +79,7 @@ private void SetProject(Project project) {
         this.project = project;
         if (project.justCreated) {
             _ = ShowPseudoScreen(new MilestonesPanel());
-        }
-
-        if (project.pages.Count == 0) {
-            ProjectPage firstPage = new ProjectPage(project, typeof(ProductionTable));
-            project.pages.Add(firstPage);
-        }
-
-        if (project.displayPages.Count == 0) {
-            project.displayPages.Add(project.pages[0].guid);
+            project.AssureFirstPage();
         }
 
         // Hack to activate all page solvers for the summary view