External engines: UCI options do not refresh

[cut1less]

Version: 2.12d
OS: Linux (installed via .sh)

Problem: When re-adding an engine like Stockfish to the list of external engines, its UCI options do not update to new defaults; new options may even be missing.

Expected behavior: Re-adding an engine should always retrigger the "uci" command, to get a fresh list of options.

[lukasmonk]

Fixed. Thanks.