Update Dockerfile

Dockerfile

@@ -1,6 +1,6 @@
 FROM debian:sid
 RUN chown root:shadow /etc/shadow; chmod 640 /etc/shadow;
-RUN chmod 2755 /sbin/unix_chkpwd || echo "文件不存在，无视"
+RUN [ -r /sbin/unix_chkpwd ] && chmod 2755 /sbin/unix_chkpwd || echo "/sbin/unix_chkpwd skipped"
 RUN useradd -d /home/user -s /bin/bash -m -u 1000 user
 RUN chown user -R /home/user; echo "cd ~" > /home/user/.bashrc;
 RUN --mount=type=secret,id=VNC_PASSWORD,mode=0444,required=true \
@@ -10,7 +10,7 @@ RUN apt update
 RUN apt install -y vim bash xfce4-terminal mate-desktop-environment-extras aqemu sudo curl wget aria2 qemu-system-x86 htop chromium screen tigervnc-standalone-server python3-pip python3-websockify python3 git fuse libfuse2 xdotool
 RUN apt remove -y lxlock
 RUN apt remove -y light-locker xscreensaver-data xscreensaver
-RUN sed -i '/@xscreensaver -no-splash/d' /etc/xdg/lxsession/LXDE/autostart || echo "配置不存在，无视"
+RUN [ -r /etc/xdg/lxsession/LXDE/autostart] && sed -i '/@xscreensaver -no-splash/d' /etc/xdg/lxsession/LXDE/autostart || echo "/etc/xdg/lxsession/LXDE/autostart skipped"
 RUN git clone https://github.com/novnc/noVNC.git noVNC
 RUN mkdir -p /home/user/.vnc
 RUN chmod -R 777 /home/user/.vnc /tmp