[bugfix] return 400 Bad Request on more cases of malformed AS data (#2399)

internal/media/processingmedia.go

@@ -115,7 +115,7 @@ func (p *ProcessingMedia) load(ctx context.Context) (*gtsmodel.MediaAttachment,
 
 		defer func() {
 			// This is only done when ctx NOT cancelled.
-			done = err == nil || !errorsv2.Comparable(err,
+			done = err == nil || !errorsv2.IsV2(err,
 				context.Canceled,
 				context.DeadlineExceeded,
 			)