Fix two glic panel crashes

* ResizeWidget() will return no size if there is nothing to be resized (e.g. chrome://glic is loaded in a tab for dev purposes). In that case it needs to return after running the callback.
* When finding browser windows for snapping, we need to skip those that don't have GlicButton (like dev tools)

Low-Coverage-Reason: TRIVIAL_CHANGE
Bug: 382677012
Change-Id: Icaab65f487d78abb6642862c0fc0ad6d967e199a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6081974
Auto-Submit: Ian Wells <iwells@chromium.org>
Commit-Queue: Andrea Gomez <andreaxg@google.com>
Reviewed-by: Andrea Gomez <andreaxg@google.com>
Cr-Commit-Position: refs/heads/main@{#1393956}