prevent crash from missing account (MetaMask#8604)

## Explanation

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Stop crash that occurs when there is a missing entry in the
`internalAccount` object.


https://metamask.sentry.io/issues/7394639158/?project=273505&query=is%3Aunresolved%20Cannot%20read%20properties%20of%20undefined&referrer=issue-stream

https://metamask.sentry.io/issues/6977774458/?project=273505&query=is%3Aunresolved%20Cannot%20read%20properties%20of%20undefined&referrer=issue-stream

## References

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## Checklist

- [X] I've updated the test suite for new or updated code as appropriate
- [X] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [X] I've communicated my changes to consumers by [updating changelogs
for packages I've
changed](https://github.com/MetaMask/core/tree/main/docs/processes/updating-changelogs.md)
- [X] I've introduced [breaking
changes](https://github.com/MetaMask/core/tree/main/docs/processes/breaking-changes.md)
in this PR and have prepared draft pull requests for clients and
consumer packages to resolve them


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Small defensive change in a selector plus a unit test; behavior only
changes for inconsistent state where an account ID is missing.
> 
> **Overview**
> Prevents `selectAssetsBySelectedAccountGroup` from crashing when an
`accountTree` group references an account ID that is missing from
`internalAccounts` by skipping those entries during account mapping.
> 
> Adds a regression test covering the missing-account scenario and
documents the fix in the assets-controllers changelog.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
78aa9aa. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: bergarces

packages/assets-controllers/CHANGELOG.md

@@ -27,6 +27,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - Malicious tokens that slip through are caught by the periodic rescan (runs daily by default)
 - Bump `@metamask/transaction-controller` from `^64.3.0` to `^64.4.0` ([#8585](https://github.com/MetaMask/core/pull/8585))
 
+### Fixed
+
+- Fix `selectAssetsBySelectedAccountGroup` crashing when an account referenced in the account tree is missing from internal accounts ([#8604](https://github.com/MetaMask/core/pull/8604))
+
 ## [104.3.0]
 
 ### Added

packages/assets-controllers/src/selectors/token-selectors.test.ts

@@ -877,6 +877,18 @@ describe('token-selectors', () => {
       expect(result).toStrictEqual(expectedMockResult);
     });
 
+    it('skips accounts referenced in accountTree but missing from internalAccounts', () => {
+      const state = cloneDeep(mockedMergedState);
+
+      state.accountTree.wallets['entropy:01K1TJY9QPSCKNBSVGZNG510GJ'].groups[
+        'entropy:01K1TJY9QPSCKNBSVGZNG510GJ/0'
+      ].accounts.push('non-existent-account-id');
+
+      const result = selectAssetsBySelectedAccountGroup(state);
+
+      expect(result).toStrictEqual(expectedMockResult);
+    });
+
     it('returns no tokens if there is no selected account group', () => {
       const result = selectAssetsBySelectedAccountGroup({
         ...mockedMergedState,

packages/assets-controllers/src/selectors/token-selectors.ts

@@ -140,6 +140,10 @@ const selectAccountsToGroupIdMap = createAssetListSelector(
         for (const accountId of accounts) {
           const internalAccount = internalAccounts.accounts[accountId];
 
+          if (!internalAccount) {
+            continue;
+          }
+
           accountsMap[
             // TODO: We would not need internalAccounts if evmTokens state had the accountId
             internalAccount.type.startsWith('eip155')