Camera settings: No devices to select from are shown

Description of the issue:

In the camera settings, no devices to select from are appearing (see grey dropdown icons in the screenshot below).

Additional info which might be helpful for debugging:

• Jami Client for GNOME Version used: 20191209.1.4b48135 Flatpak built on 2019-12-22 18:49:21 UTC
• Linux Distribution used: DISTRIB_ID=PureOS, VERSION_ID=9.0, VERSION_CODENAME=amber
• Hardware used: Lenovo Thinkpad X1 Carbon 3rd Gen
• Can other softwares access the built in camera? Yes. Tested with Gnome Cheese and with meet.jit.si over browser.
• Reason why the flatpak version is used: There's no downloadable version for Debian Bullseye (testing) provided (see #48). PureOS is based on Debian Bullseye.