change error message for `list components` commands

[nitzantomer]

right now the functions look like this:

return fugazi.components.registry.getModule(props.path).getCommands().map(componentToStruct);

but if fugazi.components.registry.getModule(props.path) returns undefined then the error message is:

Cannot read property 'getCommands' of undefined

instead first the commands need to check whether the module exists, if not return that as an error message and only if it does continue