Fix a OTA bug on `_ota_chunk_data` (#642)
Fix a OTA bug on `_ota_chunk_data` (#642)

* fix a OTA bug

* correct a wrong comment

liamchzh/shadowsocks,magic282/shadowsocks,babykiss4ever/shadowsocks,kimw/shadowsocks,vanish87/shadowsocks,liamchzh/shadowsocks,catinred2/shadowsocks,Rand01ph/shadowsocks,michaelhe/shadowsocks,CasparLi/shadowsocks,kigawas/shadowsocks,ufownl/shadowsocks,kigawas/shadowsocks-learning,fengyie007/shadowsocks,kigawas/shadowsocks-learning,catinred2/shadowsocks,michalliu/shadowsocks,xjz19901211/shadowsocks,falseen/shadowsocks,lasting-yang/shadowsocks,shenfei/shadowsocks,CasparLi/shadowsocks,bwinhwang/shadowsocks,michaelhe/shadowsocks,kimw/shadowsocks,lasting-yang/shadowsocks,hjhjw1991/shadowsocks,fengyie007/shadowsocks,hjhjw1991/shadowsocks,xjz19901211/shadowsocks,shell909090/shadowsocks,kcyeu/shadowsocks,kigawas/shadowsocks,michalliu/shadowsocks,ufownl/shadowsocks,magic282/shadowsocks,warmchang/shadowsocks,kcyeu/shadowsocks,shenfei/shadowsocks,babykiss4ever/shadowsocks,shell909090/shadowsocks,falseen/shadowsocks,bwinhwang/shadowsocks,vanish87/shadowsocks,Rand01ph/shadowsocks,warmchang/shadowsocks