better error message when failing to specify a feature or preset

Author: myk002

agitation-rebalance.lua

@@ -326,7 +326,7 @@ end
 local function do_preset(preset_name)
     local preset = presets[preset_name]
     if not preset then
-        qerror('preset not found: ' .. preset_name)
+        qerror(('preset not found: "%s"'):format(preset_name))
     end
     utils.assign(custom_difficulty, preset)
     print('agitation-rebalance: preset applied: ' .. preset_name)
@@ -763,7 +763,7 @@ local function enable_feature(which, enabled)
     end
     local feature = state.features[which]
     if feature == nil then
-        qerror('feature not found: ' .. which)
+        qerror(('feature not found: "%s"'):format(which))
     end
     state.features[which] = enabled
     print(('feature %sabled: %s'):format(enabled and 'en' or 'dis', which))
@@ -777,9 +777,9 @@ if dfhack_flags and dfhack_flags.enable then
     else do_disable()
     end
 elseif command == 'preset' then
-    do_preset(args[1])
+    do_preset(args[1] or '')
 elseif command == 'enable' or command == 'disable' then
-    enable_feature(args[1], command == 'enable')
+    enable_feature(args[1] or '', command == 'enable')
 elseif not command or command == 'status' then
     print_status()
     return