refactor: update namespaces and improve null handling in view models and controllers

Webzine.WebApplication/Areas/Administration/Controllers/ArtisteController.cs

@@ -97,12 +97,15 @@ public class ArtisteController : Controller
     [HttpPost]
     public IActionResult Edit(ArtisteEditViewModel model)
     {
-        var artiste = new Artiste
+        var artiste = this.artisteRepository.Find(model.Id);
+
+        if (artiste == null)
         {
-            IdArtiste = model.Id,
-            Nom = model.Nom,
-            Biographie = model.Biographie,
-        };
+            return this.RedirectToAction("Index");
+        }
+
+        artiste.Nom = model.Nom;
+        artiste.Biographie = model.Biographie;
 
         this.artisteRepository.Update(artiste);