Advanced channel filters (#1748)

Adds custom channel filters complete with their own mini-language. Filters can be created in settings, and applied by clicking the three dots to open the Split menu and selecting "Set filters".

src/messages/layouts/MessageLayout.cpp

@@ -115,7 +115,6 @@ bool MessageLayout::layout(int width, float scale, MessageElementFlags flags)
 void MessageLayout::actuallyLayout(int width, MessageElementFlags flags)
 {
     this->layoutCount_++;
-
     auto messageFlags = this->message_->flags;
 
     if (this->flags.has(MessageLayoutFlag::Expanded) ||
@@ -272,6 +271,9 @@ void MessageLayout::paint(QPainter &painter, int width, int y, int messageIndex,
 void MessageLayout::updateBuffer(QPixmap *buffer, int /*messageIndex*/,
                                  Selection & /*selection*/)
 {
+    if (buffer->isNull())
+        return;
+
     auto app = getApp();
     auto settings = getSettings();