do not change clipboard content if selected text is null

src/chatlog/chatlog.cpp

@@ -520,8 +520,9 @@ void ChatLog::clear()
 void ChatLog::copySelectedText() const
 {
     QString text = getSelectedText();
-
     QClipboard* clipboard = QApplication::clipboard();
+
+    if(clipboard && !text.isNull())
         clipboard->setText(text);
 }