fix: drop upload-id-marker without key-marker in ListMultipartUploads

An upload-id-marker sent without a key-marker is ignored for the
listing, but the gateway still echoed it back in UploadIdMarker. S3
discards the parameter in that case and returns an empty
UploadIdMarker.

Clear the marker in the controller when no key-marker is given, so
every backend gets the same input and the response no longer reports
a marker that had no effect.

Fixes #2150

s3api/controllers/bucket-get.go

@@ -472,6 +472,11 @@ func (c S3ApiController) ListMultipartUploads(ctx fiber.Ctx) (*Response, error)
 	keyMarker := ctx.Query("key-marker")
 	maxUploadsStr := ctx.Query("max-uploads")
 	uploadIdMarker := ctx.Query("upload-id-marker")
+	// upload-id-marker is ignored without a key-marker,
+	// so it shouldn't be echoed back in the response either
+	if keyMarker == "" {
+		uploadIdMarker = ""
+	}
 	// context keys
 	acct := utils.ContextKeyAccount.Get(ctx).(auth.Account)
 	isRoot := utils.ContextKeyIsRoot.Get(ctx).(bool)