Crash: encode_NameValue_list called with count=21, s=NULL on worker
rejoin, causing SIGSEGV in persist_worker_hook_fun.
Root cause: free_name_val_list(xce_name_val_t***, int) accepted count by
value. It zeroed *vals (resvals_to_sched = NULL) but could not zero
nresvals_to_sched. Any caller that freed the scheduler resource snapshot
(opget.c workerlist, reply.c clusterconf, dataex.c, sched.c dispatch)
left nresvals_to_sched stale. When the worker later rejoined and the
WAL HOOK fired, the WAL encoder read count=21 with a NULL pointer.
Fix: change signature to free_name_val_list(xce_name_val_t***, int*)
so both fields are zeroed atomically. Update all 7 call sites.
