TF-475 Fix save a draft email

lib/features/composer/domain/state/save_email_as_drafts_state.dart

@@ -1,6 +1,14 @@
 import 'package:core/core.dart';
 import 'package:jmap_dart_client/jmap/mail/email/email.dart';
 
+class SaveEmailAsDraftsLoading extends UIState {
+
+  SaveEmailAsDraftsLoading();
+
+  @override
+  List<Object?> get props => [];
+}
+
 class SaveEmailAsDraftsSuccess extends UIState {
 
   final Email emailAsDrafts;

lib/features/composer/domain/usecases/save_email_as_drafts_interactor.dart

@@ -12,6 +12,7 @@ class SaveEmailAsDraftsInteractor {
 
   Stream<Either<Failure, Success>> execute(AccountId accountId, Email email) async* {
     try {
+      yield Right<Failure, Success>(SaveEmailAsDraftsLoading());
       final emailAsDrafts = await emailRepository.saveEmailAsDrafts(accountId, email);
       if (emailAsDrafts != null) {
         yield Right<Failure, Success>(SaveEmailAsDraftsSuccess(emailAsDrafts));