checker: stricter mutable reference check (fix #14803) (#14805)

vlib/term/ui/input_windows.c.v

@@ -86,7 +86,7 @@ pub fn init(cfg Config) &Context {
 	C.atexit(restore_terminal_state)
 	for code in ctx.cfg.reset {
 		os.signal_opt(code, fn (_ os.Signal) {
-			mut c := ui.ctx_ptr
+			mut c := unsafe { ui.ctx_ptr }
 			if unsafe { c != 0 } {
 				c.cleanup()
 			}