QWinRTInputContext::hideInputPanel: return early if panel is not visible

If the input panel is not visible TryHide will result in
"Failed to hide input panel. (The operation completed successfully.)".
That happens a lot in Qt's auto tests for example.

Change-Id: Ieae17e07c3646dce8f348e21f537a2455fe03461
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Miguel Costa <miguel.costa@qt.io>
Reviewed-by: Andre de la Rocha <andre.rocha@qt.io>

src/plugins/platforms/winrt/qwinrtinputcontext.cpp

@@ -205,6 +205,8 @@ void QWinRTInputContext::showInputPanel()
 void QWinRTInputContext::hideInputPanel()
 {
     qCDebug(lcQpaInputMethods) << __FUNCTION__;
+    if (!m_isInputPanelVisible)
+        return;
 
     QEventDispatcherWinRT::runOnXamlThread([&]() {
         ComPtr<IInputPane2> inputPane;