Ref T536, show text entry for overlay text messages and ignore button updates if invisible

Remark: Invisibe always caused the hiden group box to show grayed out buttons
This approach is a bit hacky as the component actually does not know about its surrounding group box

src/blackgui/overlaymessages.cpp

@@ -268,6 +268,7 @@ namespace BlackGui
     {
         ui->comp_OverlayTextMessage->setTab(tab);
         ui->comp_OverlayTextMessage->updateAtcStationsButtons();
+        ui->comp_OverlayTextMessage->showTextMessageEntry(true);
         this->setModeToOverlayTextMessage();
         this->display();
         ui->comp_OverlayTextMessage->focusTextEntry();