[qmf] Initialize messagelistmodel before processing add/remove/update…

… of messages. Contributes to JB#40471

This also removes duplicate guards of init(). The init() method
guards itself.

Upstream change is here:
https://codereview.qt-project.org/#/c/84555/

qmf/src/libraries/qmfclient/qmailmessagelistmodel.cpp

@@ -306,10 +306,8 @@ bool QMailMessageListModelPrivate::processMessagesAdded(const QMailMessageIdList
         return true;
     }
 
-    if (!_initialised) {
-        init();
-    }
-
+    init();
+
     // Find if and where these messages should be added
     if (!addMessages(ids)) {
         return false;
@@ -393,14 +391,12 @@ bool QMailMessageListModelPrivate::processMessagesUpdated(const QMailMessageIdLi
         return true;
     }
 
+    init();
+
     // Find if and where these messages should be added/removed/updated
     if (!updateMessages(ids)) {
         return false;
     }
-
-    if (!_initialised) {
-        init();
-    }
 
     return true;
 }
@@ -519,9 +515,7 @@ bool QMailMessageListModelPrivate::processMessagesRemoved(const QMailMessageIdLi
         return true;
     }
 
-    if (!_initialised) {
-        init();
-    }
+    init();
 
     // Find if and where these messages should be removed from
     if (!removeMessages(ids)) {