Error when directory doesn't exist

[cmahnke]

Found this when passing a wrong file name:

I haven't checked deeper, but in this case I passed a non existing directory:

vncdotool -s /tmp/qemu_vnc.sock capture  deb12-arm64-min.img/screenshot-20250729092226.png
unsupported image format "", choose one of ('png', 'jpg', 'jpeg', 'gif', 'bmp')

The error message is wrong