Preview Settings Browser: does not open when a custom setting is used

[astares]

In a fresh Pharo 12 image:

1. Create or load any tool with a custom setting ( a tool that uses the "<systemsettings>" pragma) like https://github.com/astares/Pharo-Pomodoro

Metacello new 
	repository: 'github://astares/Pharo-Pomodoro:main/src';
	baseline: 'Pomodoro';
	load

2. Open the Preview of the new Settings Browser from the world menu

Looks like it tries to search for an icon in the icon map

Maybe a "fallback" icon should be used so at least it is possible to open this tool when no icon is provided.

[hernanmd]

Fix proposed in pharo-spec/NewTools#734

[jecisc]

Merged

[astares]

@hernanmd Thanks!