Multiple crops on same image saves only the last crop when specifying output format

[phanav]

Hello Robert Węcławski, thank you for this amazing program.
It is the best image crop tool that I found.

I hope you will have a few minutes to fix this minor detail.
It has no critical impact on the usage.

Suppose we make multiple crops on the same original file : image.png.
Running inbac without format option gives the correct result: image1.png, image2.png, image3.png, ...
Running inbac with format option (inbac -f png) gives only one output, despite the multiple crop: image, a PNG file in the correct format but without the extension .png

Perhaps the cause lies in controller.py -> save and/or find_available_name
Maybe we can fix it like this:
controller.py -> save line 161

    if self.model.args.image_format:
        new_filename, _ = os.path.splitext(new_filename)
        new_filename = os.path.join(new_filename, self.model.args.image_format) 

Anyway, thank you for your attention and for sharing this application.