[iOS][Credential-Provider] Fix search

This CL fixes an issue where the search bar was hidden while being used,
and causing the system to enter in a infinite loop.
Also avoids iterating all the credentials when the search is empty.

Bug: 1246947
Change-Id: Ie0aa180cfe9dc68d5f54b0e70af1c235764eee33
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3143386


Auto-Submit: Javier Flores <javierrobles@chromium.org>
Commit-Queue: Robbie Gibson <rkgibson@google.com>
Reviewed-by: Robbie Gibson <rkgibson@google.com>
Cr-Commit-Position: refs/heads/main@{#918772}