Update arm_u state correctly in _ch_buck_trim
Update arm_u state correctly in _ch_buck_trim

Previously, trimming the penultimate value from a hash bucket would
leave arm_u in an inconsistent state: mug_w would be pointing at
a key-value pair in a node, but arm_u.buc_o and arm_u.inx_w were
not updated to reflect this. Correspondingly, a rare edge case could
occur where said key-value pair would not be marked cold (due to
buc_o), which is a semantic error.

ngzax/urbit,ngzax/urbit,urbit/urbit,jfranklin9000/urbit,jfranklin9000/urbit,jfranklin9000/urbit,ngzax/urbit,urbit/urbit,jfranklin9000/urbit,jfranklin9000/urbit,urbit/urbit,urbit/urbit,jfranklin9000/urbit,urbit/urbit,urbit/urbit,jfranklin9000/urbit,ngzax/urbit,ngzax/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit