fix: handle undefined values in afterChange hooks when read:false and create:true on the field level access for parents and siblings (#12664)

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### What?

Fixes a bug where `afterChange` hooks would attempt to access values for
fields that are `read: false` but `create: true`, resulting in
`undefined` values and unexpected behavior.

### Why?

In scenarios where access control allows field creation (`create: true`)
but disallows reading it (`read: false`), hooks like `afterChange` would
still attempt to operate on `undefined` values from `siblingDoc` or
`previousDoc`, potentially causing errors or skipped logic.

### How?

Adds safe optional chaining and fallback object initialization in
`promise.ts` for:
- `previousDoc[field.name]`
- `siblingDoc[field.name]`
- Group, Array, and Block field traversals

This ensures that these values are treated as empty objects or arrays
where appropriate to prevent runtime errors during traversal or hook
execution.

Fixes https://github.com/payloadcms/payload/issues/12660

---------

Co-authored-by: Niall Bambury <niall.bambury@cuckoo.co>

packages/payload/src/fields/hooks/afterChange/promise.ts

@@ -88,12 +88,12 @@ export const promise = async ({
           path: pathSegments,
           previousDoc,
           previousSiblingDoc,
-          previousValue: previousDoc[field.name!],
+          previousValue: previousDoc?.[field.name!],
           req,
           schemaPath: schemaPathSegments,
           siblingData,
           siblingFields: siblingFields!,
-          value: siblingDoc[field.name!],
+          value: siblingDoc?.[field.name!],
         })
 
         if (hookedValue !== undefined) {
@@ -226,10 +226,10 @@ export const promise = async ({
           parentPath: path,
           parentSchemaPath: schemaPath,
           previousDoc,
-          previousSiblingDoc: previousDoc[field.name] as JsonObject,
+          previousSiblingDoc: (previousDoc?.[field.name] as JsonObject) || {},
           req,
           siblingData: (siblingData?.[field.name] as JsonObject) || {},
-          siblingDoc: siblingDoc[field.name] as JsonObject,
+          siblingDoc: (siblingDoc?.[field.name] as JsonObject) || {},
         })
       } else {
         await traverseFields({
@@ -282,11 +282,11 @@ export const promise = async ({
             path: pathSegments,
             previousDoc,
             previousSiblingDoc,
-            previousValue: previousDoc[field.name],
+            previousValue: previousDoc?.[field.name],
             req,
             schemaPath: schemaPathSegments,
             siblingData,
-            value: siblingDoc[field.name],
+            value: siblingDoc?.[field.name],
           })
 
           if (hookedValue !== undefined) {
@@ -305,9 +305,9 @@ export const promise = async ({
       const isNamedTab = tabHasName(field)
 
       if (isNamedTab) {
-        tabSiblingData = (siblingData[field.name] as JsonObject) ?? {}
-        tabSiblingDoc = (siblingDoc[field.name] as JsonObject) ?? {}
-        tabPreviousSiblingDoc = (previousDoc[field.name] as JsonObject) ?? {}
+        tabSiblingData = (siblingData?.[field.name] ?? {}) as JsonObject
+        tabSiblingDoc = (siblingDoc?.[field.name] ?? {}) as JsonObject
+        tabPreviousSiblingDoc = (previousDoc?.[field.name] ?? {}) as JsonObject
       }
 
       await traverseFields({