fix(docker): handle cases where DB_PORT is not defined (pterodactyl#3808)

Co-authored-by: Alex <admin@softwarenoob.com>

Author: Wuzado

.github/docker/entrypoint.sh

@@ -55,6 +55,11 @@ else
   rm -rf /etc/nginx/http.d/default.conf
 fi
 
+if [[ -z $DB_PORT ]]; then
+  echo -e "DB_PORT not specified, defaulting to 3306"
+  DB_PORT=3306
+fi
+
 ## check for DB up before starting the panel
 echo "Checking database status."
 until nc -z -v -w30 $DB_HOST $DB_PORT