BUG/MINOR: http/filters: Be sure to wait if a filter loops in HTTP_MSG_ENDING

BUG/MINOR: http/filters: Be sure to wait if a filter loops in HTTP_MSG_ENDING

A filter can choose to loop when a HTTP message is in the state
HTTP_MSG_ENDING. But the transaction is terminated with an error if the input is
closed (CF_SHUTR set on the channel). At this step, we have received all data,
so we can wait.

So now, we also check the parser state before leaving. This fix only affects
configs that use a filter that can wait in http_forward_data or http_end
callbacks, when all data were parsed.