Wrap touch calls with if/then guards for Buster docker.

Signed-off-by: Dan Schaper <dan.schaper@pi-hole.net>

automated install/basic-install.sh

@@ -1128,8 +1128,10 @@ chooseBlocklists() {
         appendToListsFile "${choice}"
     done
     # Create an empty adList file with appropriate permissions.
-    touch "${adlistFile}"
-    chmod 644 "${adlistFile}"
+    if [ ! -f "${adlistFile}" ]; then
+        touch "${adlistFile}"
+        chmod 644 "${adlistFile}"
+    fi
 }
 
 # Accept a string parameter, it must be one of the default lists
@@ -1330,8 +1332,10 @@ installConfigs() {
         # and copy in the config file Pi-hole needs
         install -D -m 644 -T ${PI_HOLE_LOCAL_REPO}/advanced/${LIGHTTPD_CFG} "${lighttpdConfig}"
         # Make sure the external.conf file exists, as lighttpd v1.4.50 crashes without it
-        touch /etc/lighttpd/external.conf
-        chmod 644 /etc/lighttpd/external.conf
+        if [ ! -f /etc/lighttpd/external.conf ]; then
+            touch /etc/lighttpd/external.conf
+            chmod 644 /etc/lighttpd/external.conf
+        fi
         # If there is a custom block page in the html/pihole directory, replace 404 handler in lighttpd config
         if [[ -f "${PI_HOLE_BLOCKPAGE_DIR}/custom.php" ]]; then
             sed -i 's/^\(server\.error-handler-404\s*=\s*\).*$/\1"\/pihole\/custom\.php"/' "${lighttpdConfig}"