Thumbnails not shown when viewing images over http(s)://

To reproduce, write ristretto https://gitlab.xfce.org/uploads/-/system/appearance/header_logo/1/xfce.png in a shell.

The expected behaviour is for thumbnails to be shown.

moved from apps/ristretto#45 (moved)

marked this issue as related to apps/ristretto#46

The problem comes from Tumbler issuing error

No thumbnailer available for "https://gitlab.xfce.org/uploads/-/system/appearance/header_logo/1/xfce.png"

because this type of request is probably not supported.

NB: There is a bug above in the dating of the issue move: I just moved it.

added 2. Feature label

marked this issue as related to #12

removed the relation with #12