lib: fix incorrect thread list processing loops

* thread.c: (thread_timer_process,thread_process) thread_list_delete nulls
  thread->next. Loops need to save next first, or will only process the head.
  Problem noted by Lou Berger <lberger@labn.net>.
diff --git a/lib/thread.c b/lib/thread.c
index 6d3c3cb..b36c43a 100644
--- a/lib/thread.c
+++ b/lib/thread.c
@@ -972,10 +972,12 @@
 thread_timer_process (struct thread_list *list, struct timeval *timenow)
 {
   struct thread *thread;
+  struct thread *next;
   unsigned int ready = 0;
   
-  for (thread = list->head; thread; thread = thread->next)
+  for (thread = list->head; thread; thread = next)
     {
+      next = thread->next;
       if (timeval_cmp (*timenow, thread->u.sands) < 0)
         return ready;
       thread_list_delete (list, thread);
@@ -991,10 +993,12 @@
 thread_process (struct thread_list *list)
 {
   struct thread *thread;
+  struct thread *next;
   unsigned int ready = 0;
   
-  for (thread = list->head; thread; thread = thread->next)
+  for (thread = list->head; thread; thread = next)
     {
+      next = thread->next;
       thread_list_delete (list, thread);
       thread->type = THREAD_READY;
       thread_list_add (&thread->master->ready, thread);