client: Allow sending content in DONE state

client: Allow sending content in DONE state

Allow sending content even when the connection is in done state. When we
run into an error we will be in CLIENT_STATE_DONE state and have to
write some content to the client. Allow writing in normal DATA and in
DONE state.

This fixes http error 403 in LuCI.

Fixes: b3e3c05d6781 ("client: don't send stray EOF chunk on connection timeout")
Signed-off-by: Hauke Mehrtens <[email protected]>