[FedCM] Tentatively fix a crash from ShowSingleIdpFailure

The root cause is similar as a previous fix in ShowAccountsDialog, where
the UI code might synchronously resolve the request, thus clearing up
the members of the caller.

Bug: 328831812
Change-Id: I0991fc34914c9a29bfca9e23a828fe0a98bc0ff4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5366262


Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Commit-Queue: Nicolás Peña <npm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1271708}