Fix use-after-move in AccountManager

Fix use-after-move in chromeos::AccountManager::GetAccountEmailInternal
callback.

Change-Id: I463165fe2e642ffed07c5c11c26984d99daf5815
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2495060Reviewed-by: Anastasiia N <anastasiian@chromium.org>
Commit-Queue: Kush Sinha <sinhak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820199}

chromeos/components/account_manager/account_manager.cc

@@ -388,6 +388,7 @@ void AccountManager::GetAccountEmailInternal(
   auto it = accounts_.find(account_key);
   if (it == accounts_.end()) {
     std::move(callback).Run(std::string());
+    return;
   }
 
   std::move(callback).Run(it->second.raw_email);