attempt to solve redraw related hangs

a mutex didnt work out so now its spinlock guarded, hopefully this
solves the few rare cases of hanging mentioned in #31

fuf.c

@@ -59,6 +59,8 @@ handle_chld()
 static void
 handle_redraw()
 {
+	extern pthread_spinlock_t redraw_lock;
+	pthread_spin_lock(&redraw_lock);
 	sendwin();
 	srefresh();
 
@@ -71,6 +73,7 @@ handle_redraw()
 		cancel_preview();
 		refresh_layout();
 	}
+	pthread_spin_unlock(&redraw_lock);
 }
 
 static void
@@ -113,6 +116,8 @@ init()
 	init_colors();
 
 	/* init fuf */
+	extern pthread_spinlock_t redraw_lock; /* not the right place for this */
+	pthread_spin_init(&redraw_lock, PTHREAD_PROCESS_SHARED); /* , whatever */
 	handle_redraw();
 	start_load(load_items, display_load);
 	init_preview(load_preview);

inc/thr.c

@@ -14,6 +14,7 @@ pthread_t preview_backup_thr;
 pthread_cond_t run_preview = PTHREAD_COND_INITIALIZER;
 pthread_mutex_t preview_lock = PTHREAD_MUTEX_INITIALIZER;
 pthread_mutex_t preview_pid_lock = PTHREAD_MUTEX_INITIALIZER;
+pthread_spinlock_t redraw_lock;
 pid_t preview_pid[2];
 _Atomic bool items_loading = false;
 _Atomic bool pn = false;