refactor(document): replace Concat with dedicated GetAllOperations iterator

Author: Mahdigln

src/Microsoft.OpenApi/Models/OpenApiDocument.cs

@@ -867,23 +867,32 @@ static bool AddToDictionary<TValue>(IDictionary<string, TValue> dict, string key
         {
             Utils.CheckArgumentNullOrEmpty(operationId);
 
-            var allPathItems = Webhooks is not null
-                ? Paths.Values.Concat(Webhooks.Values)
-                : Paths.Values;
-
-            foreach (var pathItem in allPathItems)
+            foreach (var operation in GetAllOperations())
             {
-                if (pathItem.Operations is not null)
-                {
-                    foreach (var operation in pathItem.Operations.Values)
-                    {
-                        if (string.Equals(operation.OperationId, operationId, StringComparison.Ordinal))
-                            return operation;
-                    }
-                }
+                if (string.Equals(operation.OperationId, operationId, StringComparison.Ordinal))
+                    return operation;
             }
             return null;
         }
+
+        private IEnumerable<OpenApiOperation> GetAllOperations()
+        {
+            foreach (var pathItem in Paths.Values)
+            {
+                if (pathItem.Operations is null) continue;
+                foreach (var operation in pathItem.Operations.Values)
+                    yield return operation;
+            }
+
+            if (Webhooks is null) yield break;
+
+            foreach (var pathItem in Webhooks.Values)
+            {
+                if (pathItem.Operations is null) continue;
+                foreach (var operation in pathItem.Operations.Values)
+                    yield return operation;
+            }
+        }
     }
 
     internal class FindSchemaReferences : OpenApiVisitorBase