Fix the testAllNumericUserGroup all-numeric username

Bug: Issue 11498
Change-Id: Iee6dc050f8d1e97920c3e105af7bd2a69479dcea

src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java b/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java
index 9f139c1..59e78e0 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java
@@ -103,10 +103,11 @@
   @Override
   public GroupDescription.Basic get(AccountGroup.UUID uuid) {
     String ident = username(uuid);
-    Optional<AccountState> state;
+    Optional<AccountState> state = Optional.empty();
     if (ident.matches(ACCOUNT_ID_PATTERN)) {
       state = accountCache.get(new Account.Id(Integer.parseInt(ident)));
-    } else if (ExternalId.isValidUsername(ident)) {
+    }
+    if (!state.isPresent() && ExternalId.isValidUsername(ident)) {
       state = accountCache.getByUsername(ident);
     } else {
       return null;