Reset trackedPostpones if nothing postponed

We can't rely on workingMap.size because we're now adding the fallback
nodes eagerly to the map.

Author: sebmarkbage

packages/react-server/src/ReactFizzServer.js

@@ -3932,8 +3932,7 @@ function flushCompletedQueues(
             request.resumableState,
             request.renderState,
             request.allPendingTasks === 0 &&
-              (request.trackedPostpones === null ||
-                request.trackedPostpones.workingMap.size === 0), // TODO
+              request.trackedPostpones === null,
           );
         }
 
@@ -4030,10 +4029,7 @@ function flushCompletedQueues(
         // If we need to resume we'll write the postamble in the resume instead.
         if (
           !enablePostpone ||
-          request.trackedPostpones === null ||
-          // We check the working map instead of the root because the root could've
-          // been mutated at this point if it was passed straight through to resume().
-          request.trackedPostpones.workingMap.size === 0 // TODO
+          request.trackedPostpones === null
         ) {
           writePostamble(destination, request.resumableState);
         }
@@ -4186,6 +4182,8 @@ export function getPostponedState(request: Request): null | PostponedState {
     (trackedPostpones.rootNodes.length === 0 &&
       trackedPostpones.rootSlots === null)
   ) {
+    // Reset. Let the flushing behave as if we completed the whole document.
+    request.trackedPostpones = null;
     return null;
   }
   return {