fix(cleanVm): handle broken-er alias

@xen-orchestra/backups/_cleanVm.mjs

@@ -123,7 +123,9 @@ export async function checkAliases(
 ) {
   const aliasFound = []
   for (const alias of aliasPaths) {
-    const target = await resolveVhdAlias(handler, alias)
+    let target
+    try {
+      target = await resolveVhdAlias(handler, alias)
   
       if (!isVhdFile(target)) {
         logWarn('alias references non VHD target', { alias, target })
@@ -134,8 +136,6 @@ export async function checkAliases(
         }
         continue
       }
-
-    try {
       const { dispose } = await openVhd(handler, target)
       try {
         await dispose()