streaming: Fix uninitialized error in outgoing_file_message
streaming: Fix uninitialized error in outgoing_file_message

./streaming/messages/file_message_header.hh:63:39: error: ‘format’ is
used uninitialized in this function [-Werror=uninitialized]

glommer/scylla,dwdm/scylla,linearregression/scylla,victorbriz/scylla,glommer/scylla,rluta/scylla,respu/scylla,asias/scylla,stamhe/scylla,kjniemi/scylla,wildinto/scylla,duarten/scylla,senseb/scylla,aruanruan/scylla,rentongzhang/scylla,justintung/scylla,kjniemi/scylla,avikivity/scylla,tempbottle/scylla,acbellini/scylla,glommer/scylla,rentongzhang/scylla,aruanruan/scylla,respu/scylla,tempbottle/scylla,guiquanz/scylla,avikivity/scylla,capturePointer/scylla,shaunstanislaus/scylla,scylladb/scylla,victorbriz/scylla,linearregression/scylla,bowlofstew/scylla,dwdm/scylla,rentongzhang/scylla,justintung/scylla,eklitzke/scylla,wildinto/scylla,scylladb/scylla,raphaelsc/scylla,justintung/scylla,stamhe/scylla,scylladb/scylla,wildinto/scylla,capturePointer/scylla,capturePointer/scylla,rluta/scylla,respu/scylla,rluta/scylla,phonkee/scylla,bowlofstew/scylla,kangkot/scylla,victorbriz/scylla,linearregression/scylla,dwdm/scylla,kjniemi/scylla,scylladb/scylla,gwicke/scylla,avikivity/scylla,acbellini/scylla,eklitzke/scylla,kangkot/scylla,gwicke/scylla,raphaelsc/scylla,senseb/scylla,senseb/scylla,tempbottle/scylla,guiquanz/scylla,duarten/scylla,stamhe/scylla,raphaelsc/scylla,eklitzke/scylla,shaunstanislaus/scylla,bowlofstew/scylla,gwicke/scylla,asias/scylla,duarten/scylla,aruanruan/scylla,phonkee/scylla,shaunstanislaus/scylla,asias/scylla,acbellini/scylla,kangkot/scylla,phonkee/scylla,guiquanz/scylla