geoip air-gapped setup support single database update

[kaisecheng]

As of v7.16.2, geoip custom endpoint setup is expected user download both GeoLite2-ASN and GeoLite2-City databases manually. However, if users only use one type of database, with a single database presence in the setup script, Logstash fail with the following log.

[2022-01-03T09:59:19,835][ERROR][logstash.filters.geoip.databasemanager] undefined method `[]' for nil:NilClass {:cause=>nil, :backtrace=>["C:/elastic/logstash-7.16.1/logstash-7.16.1/x-pack/lib/filters/geoip/download_manager.rb:77:in `block in check_update'", "org/jruby/RubyArray.java:2589:in `map'", "C:/elastic/logstash-7.16.1/logstash-7.16.1/x-pack/lib/filters/geoip/download_manager.rb:75:in `check_update'", "C:/elastic/logstash-7.16.1/logstash-7.16.1/x-pack/lib/filters/geoip/download_manager.rb:48:in `fetch_database'", "C:/elastic/logstash-7.16.1/logstash-7.16.1/x-pack/lib/filters/geoip/database_manager.rb:107:in `execute_download_job'", "C:/elastic/logstash-7.16.1/logstash-7.16.1/x-pack/lib/filters/geoip/database_manager.rb:220:in `block in trigger_download'", "org/jruby/ext/thread/Mutex.java:164:in `synchronize'", "C:/elastic/logstash-7.16.1/logstash-7.16.1/x-pack/lib/filters/geoip/database_manager.rb:217:in `trigger_download'", "C:/elastic/logstash-7.16.1/logstash-7.16.1/x-pack/lib/filters/geoip/database_manager.rb:276:in `subscribe_database_path'", "C:/elastic/logstash-7.16.1/logstash-7.16.1/vendor/bundle/jruby/2.5.0/gems/logstash-filter-geoip-7.2.6-java/lib/logstash/filters/geoip.rb:181:in `select_database_path'", "C:/elastic/logstash-7.16.1/logstash-7.16.1/vendor/bundle/jruby/2.5.0/gems/logstash-filter-geoip-7.2.6-java/lib/logstash/filters/geoip.rb:109:in `register'", "org/logstash/config/ir/compiler/AbstractFilterDelegatorExt.java:75:in `register'", "C:/elastic/logstash-7.16.1/logstash-7.16.1/logstash-core/lib/logstash/java_pipeline.rb:232:in `block in register_plugins'", "org/jruby/RubyArray.java:1821:in `each'", "C:/elastic/logstash-7.16.1/logstash-7.16.1/logstash-core/lib/logstash/java_pipeline.rb:231:in `register_plugins'", "C:/elastic/logstash-7.16.1/logstash-7.16.1/logstash-core/lib/logstash/java_pipeline.rb:590:in `maybe_setup_out_plugins'", "C:/elastic/logstash-7.16.1/logstash-7.16.1/logstash-core/lib/logstash/java_pipeline.rb:244:in `start_workers'", "C:/elastic/logstash-7.16.1/logstash-7.16.1/logstash-core/lib/logstash/java_pipeline.rb:189:in `run'", "C:/elastic/logstash-7.16.1/logstash-7.16.1/logstash-core/lib/logstash/java_pipeline.rb:141:in `block in start'"]}

The workaround is to place both databases to the directory and run the setup script ./bin/elasticsearch-geoip -s YOUR_DB_DIR