[fix] handle cases where nb_master > children->length in auto layout
[fix] handle cases where nb_master > children->length in auto layout

mikkeloscar/sway,ascent12/sway,1ace/sway,sleep-walker/sway,ascent12/sway,johalun/sway,1ace/sway,4e554c4c/sway,taiyu-len/sway,mikkeloscar/sway,ptMuta/sway,4e554c4c/sway,taiyu-len/sway,SirCmpwn/sway,1ace/sway,sleep-walker/sway,taiyu-len/sway,ascent12/sway