fix(xo-web/backup): maxExportRate invalid parameters (#6768)

Introduced by dc6a13962f

CHANGELOG.unreleased.md

@@ -11,6 +11,8 @@
 
 > Users must be able to say: “I had this issue, happy to know it's fixed”
 
+- [Backup] Fix `Invalid parameters` when deleting `speed limit` value (PR [#6768](https://github.com/vatesfr/xen-orchestra/pull/6768))
+
 ### Packages to release
 
 > When modifying a package, add it here with its release type.
@@ -27,6 +29,7 @@
 
 <!--packages-start-->
 
+- xo-web patch
 - xo-server minor
 
 <!--packages-end-->

packages/xo-web/src/xo-app/backup/new/index.js

@@ -610,7 +610,7 @@ const New = decorate([
       },
       setMaxExportRate({ setGlobalSettings }, rate) {
         setGlobalSettings({
-          maxExportRate: rate * (1024 * 1024),
+          maxExportRate: rate !== undefined ? rate * (1024 * 1024) : undefined,
         })
       },
       setOfflineBackup: