conversationmodel: fix reloading for merge commits

if the cache is cleaned but not the latest interaction, when
reloading, if the lastMessageUid is a merge commit, it will
not reload until the latest interaction

jami-client-qt#340

Change-Id: I91ade5b2e80957bb97fe711e95f2837330553b0e

src/conversationmodel.cpp

@@ -1392,8 +1392,9 @@ ConversationModel::clearInteractionsCache(const QString& convId)
                 std::lock_guard<std::mutex> lk(pimpl_->interactionsLocks[convId]);
                 conversation.interactions->clear();
             }
-            ConfigurationManager::instance().loadConversationMessages(owner.id, convId, "", 1);
             conversation.allMessagesLoaded = false;
+            conversation.lastMessageUid = "";
+            ConfigurationManager::instance().loadConversationMessages(owner.id, convId, "", 1);
         }
     } catch (const std::out_of_range& e) {
         qDebug() << "can't find interaction from conversation: " << e.what();