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/SplitInput.cpp

@@ -8,6 +8,7 @@
 #include "singletons/Settings.hpp"
 #include "singletons/Theme.hpp"
 #include "util/Clamp.hpp"
+#include "util/Helpers.hpp"
 #include "util/LayoutCreator.hpp"
 #include "widgets/Notebook.hpp"
 #include "widgets/Scrollbar.hpp"
@@ -568,8 +569,10 @@ void SplitInput::insertCompletionText(const QString &input_)
         }
         else if (text[i] == '@')
         {
-            input = "@" + input_ +
-                    (getSettings()->mentionUsersWithComma ? ", " : " ");
+            const auto userMention =
+                formatUserMention(input_, edit.isFirstWord(),
+                                  getSettings()->mentionUsersWithComma);
+            input = "@" + userMention + " ";
             done = true;
         }
 
@@ -595,6 +598,11 @@ void SplitInput::clearSelection()
     this->ui_.textEdit->setTextCursor(c);
 }
 
+bool SplitInput::isEditFirstWord() const
+{
+    return this->ui_.textEdit->isFirstWord();
+}
+
 QString SplitInput::getInputText() const
 {
     return this->ui_.textEdit->toPlainText();