_UpdateMirrorIfNotContains populates the mirror if a given rev
isn't found in the mirror, but if this rev is invalid, it's never
fetched at all. Check that we've actually fetched it after
populating the mirror.
Bug: 407864212
Change-Id: Id66695636e749c4f7372aa522ab03ec4ec8feb52
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6441962
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>