Simplify backgrounds diversion, now that there's only one file

debian/kali-themes.postinst

@@ -107,15 +107,15 @@ if [ "$1" = "configure" ]; then
 	# Install remaining new files
 	install_all
     fi
-    # Disable some backgrounds in Gnome and KDE
-    while read file; do
-        mkdir -p "$(dirname $file)/disabled"
-        dpkg-divert --rename --package kali-themes \
-                             --divert "$(dirname $file)/disabled/$(basename $file)" \
-                             --add "$file"
-    done << EOF
-/usr/share/gnome-background-properties/gnome-backgrounds.xml
-EOF
+    # Disable GNOME backgrounds
+    file=/usr/share/gnome-background-properties/gnome-backgrounds.xml
+    if [ -e $file ]; then
+	diverted_file=$(dirname $file)/disabled/$(basename $file)
+	mkdir -p "$(dirname $diverted_file)"
+	dpkg-divert --rename --package kali-themes \
+		    --divert "$diverted_file" \
+		    --add "$file"
+    fi
     # Configure /root/.face to have a red-background avatar
     if [ ! -e /root/.face ]; then
         cp /usr/share/kali-themes/.face-root.svg /root/.face