Enable hotkeys after setting them in virt_viewer_app_set_hotkeys
    
    Enabling hotkeys will trigger a rebuild of the 'send keys' menu
    containing the new hotkeys. virt_viewer_app_set_hotkeys() was clearing
    and then enabling the hotkeys before parsing the string containing the
    new hotkeys. This was causing these hotkeys to be missing from the 'Send
    keys' menu when they are set through the spice controller because the
    'send keys' menu was rebuilt before the new hotkeys are set.
    
    Resolves: rhbz#1055600