tests: Fix test execution if only one language is configured

test_languagePopupListActiveLocales test will fail with
unhandled exception if only Korean (for example) is configured.

In this case the language button is not found, and calling
virtualKeyClick() function with null parameter causes an
unhandled exception.

Change-Id: Idc5d57fe56423d7a49947f6c02e75d28b7e4ec90
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

tests/auto/inputpanel/data/inputpanel/inputpanel.qml

@@ -368,6 +368,8 @@ InputPanel {
     }
 
     function virtualKeyPress(key) {
+        if (!key)
+            return false
         return multiLayoutKeyActionHelper(key, virtualKeyPressOnCurrentLayout)
     }