generics: generic call inside generic call; checker: check mut args at call

vlib/sync/pool.v

@@ -116,7 +116,7 @@ pub fn (mut pool PoolProcessor) work_on_pointers(items []voidptr) {
 	pool.thread_contexts << [voidptr(0)].repeat(pool.items.len)
 	pool.waitgroup.add(njobs)
 	for i := 0; i < njobs; i++ {
-		go process_in_thread(pool,i)
+		go process_in_thread(mut pool,i)
 	}
 	pool.waitgroup.wait()
 }