fix various warnings

src/messages/layouts/MessageLayout.cpp

@@ -27,7 +27,6 @@ namespace chatterino {
 
 MessageLayout::MessageLayout(MessagePtr message)
     : message_(message)
-    , buffer_(nullptr)
     , container_(std::make_shared<MessageLayoutContainer>())
 {
     DebugCount::increase("message layout");

src/messages/layouts/MessageLayout.hpp

@@ -65,7 +65,7 @@ private:
     // variables
     MessagePtr message_;
     std::shared_ptr<MessageLayoutContainer> container_;
-    std::shared_ptr<QPixmap> buffer_ = nullptr;
+    std::shared_ptr<QPixmap> buffer_{};
     bool bufferValid_ = false;
 
     int height_ = 0;