Fixed comma appended to username completion when not at the beginning of the message (#3060)

Co-authored-by: pajlada <rasmus.karlsson@pajlada.com>

src/widgets/splits/Split.hpp

@@ -47,6 +47,7 @@ public:
     pajlada::Signals::NoArgSignal focusLost;
 
     ChannelView &getChannelView();
+    SplitInput &getInput();
 
     IndirectChannel getIndirectChannel();
     ChannelPtr getChannel();