nixos/octoprint: fix setting host causing port to be unset

This was because of the non-recursive update of the attrset.

nixos/modules/services/misc/octoprint.nix

···
 
   cfg = config.services.octoprint;
 
-  baseConfig = {
+  baseConfig = lib.recursiveUpdate {
     plugins.curalegacy.cura_engine = "${pkgs.curaengine_stable}/bin/CuraEngine";
     server.port = cfg.port;
     webcam.ffmpeg = "${pkgs.ffmpeg.bin}/bin/ffmpeg";
-  } // lib.optionalAttrs (cfg.host != null) { server.host = cfg.host; };
+  } (lib.optionalAttrs (cfg.host != null) { server.host = cfg.host; });
 
   fullConfig = lib.recursiveUpdate cfg.extraConfig baseConfig;