`addCustomLoadOverride` and `addCustomSaveOverride` callbacks require a return value

[tdulcet]

The AutomaticSettings.Trigger.addCustomLoadOverride() and AutomaticSettings.Trigger.addCustomSaveOverride() callbacks require a return value. The README says:

By default, the library assumes you now handle loading and saving by yourself, i.e. you need to interact with the HTML DOM (for loading) or the storage API (for saving) directly.

which implies that a return value should not be required. However, not providing the return value results in an exception, which prevents the options page from fully loading:

The issue is several lines like this:

AutomaticSettings/internal/Trigger.js

Lines 261 to 263 in fce7d28

	// destructure data, if it has been returned, so next call can
	// potentially also use it
	if (result.command === CONTINUE_RESULT) {

that do not first check that the result from the callback is defined before using it.

[rugk]

Yeah hmm… sounds reasonable. So what should happen if you return no value? (Just ignore all further handling I guess?)

Looking at the doc, I see that I guess I mostly used it with AutomaticSettings.Trigger.overrideContinue.overrideContinue and your use case was never really tested.

So a PR is very well appreciated.