Potential fix for code scanning alert no. 82: Missed opportunity to use Where

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

Author: vb2ae

src/Caliburn.Micro.Core/SimpleContainer.cs

@@ -181,12 +181,9 @@ public IEnumerable<object> GetAllInstances(Type service, string key = null)
 
             var instances = currentEntry.Select(e => e(this));
 
-            foreach (var instance in instances)
+            foreach (var instance in instances.Where(instance => EnablePropertyInjection && instance != null))
             {
-                if (EnablePropertyInjection && instance != null)
-                {
-                    BuildUp(instance);
-                }
+                BuildUp(instance);
             }
 
             return instances;