after startTransfer the transfer, and thus downloadState, is gone. asan
hasn't caught this, presumably because the access is in libc somewhere.
we don't even need access to the old state; the assertion is not useful
here and clearing the previous exception is invisible to the new round.
Change-Id: I32dc1a487b96cbaabcf5061c9b1f96dbc5aaae49
eldritch horrors
fafe647bc2