Videos keep playing after one fails to load, and other fixes

Fixes

• A player no longer crashes when its screen’s location comes without coordinates.
• USB capture devices that send uncompressed video now play.
• A scheduling rule that fails while it’s being checked no longer restarts the player in a loop.
• After 1 video fails to load, the rest of the videos still play.
• A player no longer hangs while closing a video, or restarts onto a video it has already dropped.
• A web page that’s still on screen is no longer dropped from the player’s memory.
• Scheduled content no longer builds up in the player’s memory with each content update.
• 1 diagnostics check timing out now reports 1 failure instead of up to 3.
• Repeated Wi-Fi scans in the Wi-Fi settings no longer pile up and time out early.
• A stalled connection to Screenly no longer holds up every request behind it.
• 1 unreadable USB device no longer stops the player listing the others.

Improvements

• A new power-off command, which the dashboard sends from “Power off” on a screen’s Actions tab since Screenly 26.10.4.
• The disk image and the Raspberry Pi Imager entry are called ScreenlyOS, so what you flash has the same name as what runs. The fixed download address follows the new name: screenlyos-latest-pi64-stable.img.zip for Raspberry Pi and screenlyos-latest-x86-stable.img.zip for x86. The old screenly-latest address no longer updates, so a bookmark or script that uses it needs the new one.
• Dependencies and system libraries updated.