Fix update "move all to trash" action.

Bug found by Allen

src/kmmainwidget.cpp

@@ -3890,10 +3890,7 @@ void KMMainWidget::slotAkonadiStandardActionUpdated()
                         && folderWithContent);
     }
 
-    if (QAction *act = mAkonadiStandardActionManager->action(Akonadi::StandardMailActionManager::MoveAllToTrash)) {
-        act->setEnabled(folderWithContent && (mCurrentFolderSettings->count() > 0) && mCurrentFolderSettings->canDeleteMessages());
-        act->setText((mCurrentFolderSettings && CommonKernel->folderIsTrash(mCurrentCollection)) ? i18n("E&mpty Trash") : i18n("&Move All Messages to Trash"));
-    }
+    updateMoveAllToTrash();
 
     QList<QAction *> addToFavorite;
     QAction *actionAddToFavoriteCollections = akonadiStandardAction(Akonadi::StandardActionManager::AddToFavoriteCollections);
@@ -3992,6 +3989,8 @@ void KMMainWidget::updateFolderMenu()
 
     const bool isInTrashFolder = (mCurrentFolderSettings && CommonKernel->folderIsTrash(mCurrentCollection));
     QAction *moveToTrash = akonadiStandardAction(Akonadi::StandardMailActionManager::MoveToTrash);
+    updateMoveAllToTrash();
+
     KMail::Util::setActionTrashOrDelete(moveToTrash, isInTrashFolder);
 
     mTrashThreadAction->setIcon(isInTrashFolder ? QIcon::fromTheme(QStringLiteral("edit-delete-shred")) : QIcon::fromTheme(QStringLiteral("edit-delete")));
@@ -4040,6 +4039,15 @@ void KMMainWidget::updateFolderMenu()
     }
 }
 
+void KMMainWidget::updateMoveAllToTrash()
+{
+    if (QAction *act = mAkonadiStandardActionManager->action(Akonadi::StandardMailActionManager::MoveAllToTrash)) {
+        const bool folderWithContent = mCurrentFolderSettings && !mCurrentFolderSettings->isStructural();
+        act->setEnabled(folderWithContent && (mCurrentFolderSettings->count() > 0) && mCurrentFolderSettings->canDeleteMessages());
+        act->setText((mCurrentFolderSettings && CommonKernel->folderIsTrash(mCurrentCollection)) ? i18n("E&mpty Trash") : i18n("&Move All Messages to Trash"));
+    }
+}
+
 //-----------------------------------------------------------------------------
 void KMMainWidget::slotIntro()
 {

src/kmmainwidget.h

@@ -532,6 +532,7 @@ private:
     void slotHistorySwitchFolder(const Akonadi::Collection &collection);
     void redoSwitchFolder();
     void undoSwitchFolder();
+    void updateMoveAllToTrash();
 
     // Message actions
     QAction *mDeleteAction = nullptr;