Skip panic on rangetree_destroy

Documented in Issue #361 but reason as of yet unknown, but as it is
house-keeping panic it is better the users do not experience crashes.

module/zfs/range_tree.c

@@ -150,7 +150,15 @@ range_tree_create(range_tree_ops_t *ops, void *arg, kmutex_t *lp)
 void
 range_tree_destroy(range_tree_t *rt)
 {
-	VERIFY0(rt->rt_space);
+	/*
+	 * Issue #361. The tester framework can trigger this panic quite readily
+	 * and we are unsure why. Since it is a release-time-clean-code panic
+	 * we will live without it, so that users do not experience crashes.
+	 */
+	//VERIFY0(rt->rt_space);
+	if (rt->rt_space != 0) {
+		printf("ZFS: Issue #361 triggered: rt_space == %llu\n", rt->rt_space);
+	}
 
 	if (rt->rt_ops != NULL)
 		rt->rt_ops->rtop_destroy(rt, rt->rt_arg);