[PWA/NavCapture] Don't capture navigations to invalid URLs.

Somehow it seems session restore sometimes tries to navigate to
invalid URLs. To avoid CHECK-failing for this, simply don't try
to navigation capture these navigations, as there won't be anything
to capture anyway.

Bug: 379623448
Change-Id: Ie90015913b393ff7822a66d7b7c62c929d066d77
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6036350
Auto-Submit: Marijn Kruisselbrink <mek@chromium.org>
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Reviewed-by: Dibyajyoti Pal <dibyapal@chromium.org>
Commit-Queue: Dibyajyoti Pal <dibyapal@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1385277}