Fix loading local accounts with extraneous domain part in WebUI (#28559)

app/javascript/mastodon/reducers/accounts_map.js

@@ -2,8 +2,13 @@ import { Map as ImmutableMap } from 'immutable';
 
 import { ACCOUNT_LOOKUP_FAIL } from '../actions/accounts';
 import { importAccounts } from '../actions/accounts_typed';
+import { domain } from '../initial_state';
 
-export const normalizeForLookup = str => str.toLowerCase();
+export const normalizeForLookup = str => {
+  str = str.toLowerCase();
+  const trailingIndex = str.indexOf(`@${domain.toLowerCase()}`);
+  return (trailingIndex > 0) ? str.slice(0, trailingIndex) : str;
+};
 
 const initialState = ImmutableMap();