luci-base: fix handling of large ubus HTTP requests
luci-base: fix handling of large ubus HTTP requests

Properly handle ubus POST requests exceeding the default chunk size
and fix a possible nil dereference when rejecting incoming requests
due to bad JSON message framing.

Signed-off-by: Jo-Philipp Wich <bd73d35759d75cc215150d1bbc94f1b1078bee01@mein.io>

tobiaswaldvogel/luci,rogerpueyo/luci,hnyman/luci,hnyman/luci,openwrt/luci,openwrt/luci,openwrt/luci,tobiaswaldvogel/luci,lbthomsen/openwrt-luci,openwrt/luci,Noltari/luci,nmav/luci,hnyman/luci,nmav/luci,lbthomsen/openwrt-luci,rogerpueyo/luci,tobiaswaldvogel/luci,artynet/luci,rogerpueyo/luci,nmav/luci,hnyman/luci,lbthomsen/openwrt-luci,nmav/luci,rogerpueyo/luci,Noltari/luci,tobiaswaldvogel/luci,lbthomsen/openwrt-luci,Noltari/luci,hnyman/luci,artynet/luci,artynet/luci,nmav/luci,artynet/luci,rogerpueyo/luci,Noltari/luci,nmav/luci,tobiaswaldvogel/luci,artynet/luci,Noltari/luci,nmav/luci,lbthomsen/openwrt-luci,hnyman/luci,lbthomsen/openwrt-luci,artynet/luci,artynet/luci,rogerpueyo/luci,tobiaswaldvogel/luci,nmav/luci,lbthomsen/openwrt-luci,rogerpueyo/luci,tobiaswaldvogel/luci,openwrt/luci,rogerpueyo/luci,Noltari/luci,hnyman/luci,openwrt/luci,Noltari/luci,lbthomsen/openwrt-luci,artynet/luci,Noltari/luci,openwrt/luci,hnyman/luci,openwrt/luci,Noltari/luci,nmav/luci,tobiaswaldvogel/luci,artynet/luci