[Passwords] Fix crash in IsAccountStore() when there is login_db_

This issues has been surfaced in crrev.com/c/2364508.
Details are in the linked bug

Bug: 1119758
Change-Id: Id973f22c31a37853351034ac1d449f6e7afed396
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2366740Reviewed-by: Jan Wilken Dörrie <jdoerrie@chromium.org>
Commit-Queue: Mohamed Amir Yosef <mamir@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800105}

components/password_manager/core/browser/password_store_default.cc

@@ -355,7 +355,7 @@ PasswordStoreSync::MetadataStore* PasswordStoreDefault::GetMetadataStore() {
 }
 
 bool PasswordStoreDefault::IsAccountStore() const {
-  return login_db_->is_account_store();
+  return login_db_ && login_db_->is_account_store();
 }
 
 bool PasswordStoreDefault::DeleteAndRecreateDatabaseFile() {