Move changeSubscription for _document to finally to mirror page handl…

…ing in Turbopack (vercel#59664)

## What?

Moves the changeSubscription for _document into the finally block,
similar to how the page itself is handled there as well.
This should allow moving the rest of the try block into a separate
function that can be reused for builds too.


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Closes NEXT-1885

packages/next/src/server/lib/router-utils/setup-dev-bundler.ts

@@ -1563,16 +1563,6 @@ async function startWatcher(opts: SetupOpts) {
                     '_document',
                     await globalEntries.document.writeToDisk()
                   )
-
-                  changeSubscription(
-                    '_document',
-                    'server',
-                    false,
-                    globalEntries.document,
-                    () => {
-                      return { action: HMR_ACTIONS_SENT_TO_BROWSER.RELOAD_PAGE }
-                    }
-                  )
                   processIssues('_document', writtenEndpoint)
                 }
                 await loadPagesManifest('_document')
@@ -1620,6 +1610,17 @@ async function startWatcher(opts: SetupOpts) {
                     }
                   }
                 )
+                if (globalEntries.document) {
+                  changeSubscription(
+                    '_document',
+                    'server',
+                    false,
+                    globalEntries.document,
+                    () => {
+                      return { action: HMR_ACTIONS_SENT_TO_BROWSER.RELOAD_PAGE }
+                    }
+                  )
+                }
               }
 
               break