Support rendering image reactions for mxc keys

Beeper clients only use an mxc url as reaction key when sending image
reactions, instead of properly setting the url field.

src/customisations/models/IMediaEventContent.ts

@@ -100,6 +100,13 @@ export function prepEventContentAsMedia(content: Partial<IMediaEventContent>): I
             mxc: content.file.url,
             file: content.file,
         };
+    } else if (content["m.relates_to"]?.key?.startsWith("mxc://")) {
+        // Fallback to key, since some clients only set the key to the mxc:// url while omitting the actual url field for reactions
+        return {
+            thumbnail,
+            mxc: content["m.relates_to"]?.key,
+            file: content.file,
+        };
     }
 
     throw new Error("Invalid file provided: cannot determine MXC URI. Has it been redacted?");

src/utils/MediaEventHelper.ts

@@ -118,6 +118,10 @@ export class MediaEventHelper implements IDestroyable {
         const mediaMsgTypes: string[] = [MsgType.Video, MsgType.Audio, MsgType.Image, MsgType.File];
         if (mediaMsgTypes.includes(content.msgtype!)) return true;
         if (typeof content.url === "string") return true;
+        if (event.getType() === EventType.Reaction && content["m.relates_to"]?.key?.startsWith("mxc://")) {
+            // Some clients only send mxc url as key, without setting the url field
+            return true;
+        }
 
         // Finally, it's probably not media
         return false;