input: don't drop a keystroke on the floor when the terminal resizes

This fixes the first part of https://savannah.gnu.org/bugs/?48331

.
Reported-by: Mike Frysinger <vapier@gentoo.org>

src/winio.c

@@ -141,8 +141,10 @@ void get_key_buffer(WINDOW *win)
     input = wgetch(win);
 
 #ifndef NANO_TINY
-    if (the_window_resized())
+    if (the_window_resized()) {
+	ungetch(input);
 	input = KEY_WINCH;
+    }
 #endif
 
     if (input == ERR && nodelay_mode)