Instead of selecting the base URL initially or when a load error occurs,
it is now selected when a chunk or initialization chunk is created. The
selected base URL is then assigned to
`RepresentationHolder.lastUsedBaseUrl` that is excluded in case of a
load error. For a next chunk another base URL will be selected by using
the `BaseUrlExclusionList`.
PiperOrigin-RevId: 395721221
