Pasting images fails if clipboard also offers text/uri-list

[WhyNotHugo]

When my screenshot application copies files into the clipboard selection, it offers two mime-types:

• image/png (where the accepting application gets a stream of bytes).
• text/uri-list (where the accepting application gets a path to a file).

It only image/png is offered, Signal will paste fine. But if both are offered Signal always attempts to paste reading the file. This fails due to Signal being sandboxed, and since it doesn't try the other mime-type, it just hands indefinitely due to a failure reading the file.

I'm not entirely sure how/if this can be fixed without tampering upstream, but since upstream indicates that Flathub-specific issues belong here, I figured it's best to start reporting this here.