build(browser-desktop): guard APT_MIRROR rewrite when debian.sources is absent

Co-Authored-By: Claude Fable 5.1 <[email protected]>

docker/browser-desktop/Dockerfile

@@ -19,7 +19,7 @@ ARG APT_MIRROR=
 # 1 = 装容器内输入法 fcitx5(拼音 + mozc,缺省装;是否启动由运行时 UMT_DESKTOP_IME=fcitx5 决定)
 ARG WITH_FCITX5=1
 
-RUN if [ -n "$APT_MIRROR" ]; then sed -i "[email protected]@${APT_MIRROR}@g" /etc/apt/sources.list.d/debian.sources; fi \
+RUN if [ -n "$APT_MIRROR" ]; then for f in /etc/apt/sources.list.d/debian.sources /etc/apt/sources.list; do [ -f "$f" ] && sed -i "[email protected]@${APT_MIRROR}@g" "$f"; done; fi \
   && apt-get update \
   && apt-get install -y --no-install-recommends \
     libdbus-glib-1-2 libxt6t64 libasound2t64 libx11-xcb1 libxcomposite1 libxcursor1 libxdamage1 libxfixes3 \