Only update the storage on levels that exist.  Especially helps for cube
maps which have 90 images that would be iterated over in all cases.  Added
an additional early-out check if the image is dirty for cube maps to match
the other texture types.

BUG=260069

Change-Id: I3d298f4f9ebdc23136a31138a3ef8364667fa78c
Reviewed-on: https://chromium-review.googlesource.com/199344Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Nicolas Capens <nicolascapens@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>