Set MessageViewer::Viewer::setFolderIdentity when displaying an email.

src/kmreaderwin.cpp

@@ -25,6 +25,7 @@
 #include <PimCommon/BroadcastStatus>
 #include "kmcommands.h"
 #include <MailCommon/SendMdnHandler>
+#include <MailCommon/MailUtil>
 #include <QVBoxLayout>
 #include <MessageViewer/HeaderStrategy>
 #include <MessageViewer/MarkMessageReadHandler>
@@ -677,11 +678,13 @@ void KMReaderWin::clear(bool force)
 void KMReaderWin::setMessage(const Akonadi::Item &item, MimeTreeParser::UpdateMode updateMode)
 {
     qCDebug(KMAIL_LOG) << Q_FUNC_INFO << parentWidget();
+    mViewer->setFolderIdentity(MailCommon::Util::folderIdentity(item));
     mViewer->setMessageItem(item, updateMode);
 }
 
 void KMReaderWin::setMessage(const KMime::Message::Ptr &message)
 {
+    mViewer->setFolderIdentity(0);
     mViewer->setMessage(message);
 }