luci-base: handle potential crash in luci.model.network.interface.get_i18n()
luci-base: handle potential crash in luci.model.network.interface.get_i18n()

Should prevent the crash mentioned in #1779.

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

chris5560/openwrt-luci,Noltari/luci,nmav/luci,rogerpueyo/luci,Noltari/luci,hnyman/luci,kuoruan/luci,chris5560/openwrt-luci,lbthomsen/openwrt-luci,Noltari/luci,nmav/luci,rogerpueyo/luci,openwrt/luci,openwrt-es/openwrt-luci,tobiaswaldvogel/luci,lbthomsen/openwrt-luci,wongsyrone/luci-1,artynet/luci,hnyman/luci,nmav/luci,chris5560/openwrt-luci,openwrt/luci,openwrt/luci,kuoruan/lede-luci,openwrt-es/openwrt-luci,chris5560/openwrt-luci,chris5560/openwrt-luci,kuoruan/lede-luci,kuoruan/luci,nmav/luci,tobiaswaldvogel/luci,artynet/luci,openwrt-es/openwrt-luci,tobiaswaldvogel/luci,tobiaswaldvogel/luci,nmav/luci,nmav/luci,wongsyrone/luci-1,kuoruan/luci,artynet/luci,openwrt/luci,artynet/luci,openwrt-es/openwrt-luci,kuoruan/luci,artynet/luci,openwrt-es/openwrt-luci,nmav/luci,hnyman/luci,openwrt-es/openwrt-luci,openwrt/luci,hnyman/luci,lbthomsen/openwrt-luci,kuoruan/lede-luci,artynet/luci,kuoruan/lede-luci,tobiaswaldvogel/luci,openwrt/luci,openwrt/luci,openwrt-es/openwrt-luci,kuoruan/luci,artynet/luci,nmav/luci,wongsyrone/luci-1,Noltari/luci,openwrt/luci,hnyman/luci,tobiaswaldvogel/luci,lbthomsen/openwrt-luci,rogerpueyo/luci,hnyman/luci,kuoruan/lede-luci,chris5560/openwrt-luci,kuoruan/lede-luci,hnyman/luci,tobiaswaldvogel/luci,nmav/luci,tobiaswaldvogel/luci,kuoruan/luci,wongsyrone/luci-1,chris5560/openwrt-luci,Noltari/luci,rogerpueyo/luci,wongsyrone/luci-1,hnyman/luci,kuoruan/luci,artynet/luci,chris5560/openwrt-luci,Noltari/luci,lbthomsen/openwrt-luci,wongsyrone/luci-1,Noltari/luci,Noltari/luci,rogerpueyo/luci,lbthomsen/openwrt-luci,Noltari/luci,wongsyrone/luci-1,lbthomsen/openwrt-luci,rogerpueyo/luci,rogerpueyo/luci,kuoruan/lede-luci,lbthomsen/openwrt-luci,rogerpueyo/luci,kuoruan/luci,artynet/luci,openwrt-es/openwrt-luci,kuoruan/lede-luci,wongsyrone/luci-1