Fix a crash when sitting around with no room open

This doesn't check if m_room is null before accessing it's connection.
You can easily reproduce this by sitting around leaving NeoChat open
without entering a room.

src/models/messagecontentmodel.cpp

@@ -578,8 +578,8 @@ MessageComponent MessageContentModel::linkPreviewComponent(const QUrl &link)
     }
     if (linkPreviewer->loaded()) {
         return MessageComponent{MessageComponentType::LinkPreview, QString(), {{"link"_ls, link}}};
-    } else {
+    }
-        connect(linkPreviewer, &LinkPreviewer::loadedChanged, [this, link]() {
+    connect(linkPreviewer, &LinkPreviewer::loadedChanged, this, [this, link]() {
         const auto linkPreviewer = dynamic_cast<NeoChatConnection *>(m_room->connection())->previewerForLink(link);
         if (linkPreviewer != nullptr && linkPreviewer->loaded()) {
             for (auto &component : m_components) {
@@ -594,7 +594,6 @@ MessageComponent MessageContentModel::linkPreviewComponent(const QUrl &link)
     });
     return MessageComponent{MessageComponentType::LinkPreviewLoad, QString(), {{"link"_ls, link}}};
 }
-}
 
 QList<MessageComponent> MessageContentModel::addLinkPreviews(QList<MessageComponent> inputComponents)
 {

src/models/messageeventmodel.cpp

@@ -84,7 +84,6 @@ void MessageEventModel::setRoom(NeoChatRoom *room)
         return;
     }
 
-    if (m_currentRoom) {
     // HACK: Reset the model to a null room first to make sure QML dismantles
     // last room's objects before the room is actually changed
     beginResetModel();
@@ -98,7 +97,6 @@ void MessageEventModel::setRoom(NeoChatRoom *room)
     m_contentModels.clear();
     m_reactionModels.clear();
     m_readMarkerModels.clear();
-    }
 
     beginResetModel();
     m_currentRoom = room;