Not always possible to change the frame range from the GUI

[jafyvilla]

If Livre is initialized with a specific frame range, e.g. --frames '200 300' and then the user wants to change this from the livreGUI, depending on the change the GUI animation component gets disabled.

For example, the initial frame range is [200, 300), and the user wants to change it to [200, 250). As soon as the first '2' in '250' is typed, the frame range [200, 2) is processed. Since '2' is not a valid frame in the initial frame range (it is outside the valid range of values), the whole animation component in the GUI is disabled, making it impossible to continue typing or changing frame-related parameters.