checker: disallow struct int to ptr outside unsafe (#17923)

vlib/net/unix/common.v

@@ -42,7 +42,7 @@ fn @select(handle int, test Select, timeout time.Duration) !bool {
 	// infinite timeout is signaled by passing null as the timeout to
 	// select
 	if timeout == unix.infinite_timeout {
-		timeval_timeout = &C.timeval(0)
+		timeval_timeout = &C.timeval(unsafe { nil })
 	}
 
 	match test {