shouldRetry treated every Code=200501 API error as a transient storage
block error and retried it. Proton also returns Code=200501 with an
HTTP 422 for permanent validation failures (e.g. a content key packet
that cannot be verified, or an upload format the account is not
enabled for), so these were retried until the operation timed out
causing a multi-minute hang.
This fixes it by only retrying Code=200501 when it is not a permanent
client (4xx) error.
Nick Craig-Wood
4235aa4fe5