Fix QCompleter popup regression

The PR #8129 has introduced a regression with the QCompleter popup in
the Debug window.

How to reproduce:
  1) open the Debug window;
  2) go to the 'Console' tab;
  3) start writing some rpc command and try to pick it from the list
using arrow keys, press Enter.
Note that the popup used to display completions is not being closed. To
close it they should mouse click somewhere outside of the popup.

src/qt/rpcconsole.cpp

@@ -536,6 +536,7 @@ bool RPCConsole::eventFilter(QObject* obj, QEvent *event)
             // forward these events to lineEdit
             if(obj == autoCompleter->popup()) {
                 QApplication::postEvent(ui->lineEdit, new QKeyEvent(*keyevt));
+                autoCompleter->popup()->hide();
                 return true;
             }
             break;