Don't yield empty iteration scopes

[AndreasArvidsson]

Or should we just hide them from the scope fixtures?

@pokey Can you see any problems with ignoring empty iteration scopes?

[saidelike]

Do you have an example of situation when this happens?

[AndreasArvidsson]

Where we have an empty iteration scope? eg foo(). You can also look at the changed files in #2968 for more examples.