Mishandling of <img srcset=...>

[pbryan]

Description
Foliate is not rendering an image when the img tag contains the srcset attribute, even when there is a src attribute present. When the srcset attribute is removed, the image renders correctly.

To Reproduce
Steps to reproduce the behavior:

1. Open title with srcset attribute present in image(s).
2. Open title without srcset attributes present.
3. Compare and observe missing images in the former.

Version:

• Foliate version: 3.3.0
• OS/Distribution and version: Arch Linux
• Desktop environment: GNOME 50
• Installation method: Flatpak

Additional context

• Public domain title with srcset: https://pbryan.sdf.org/abbot-flatland-with-srcset.epub
• Same title without srcset: https://pbryan.sdf.org/abbot-flatland-without-srcset.epub