sortBy doesn't work if it's on its own

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sortBy / sortByDescending does not work if it is the only expression in the query eg

query { for x in y do
        sortByDescending x.z
        head }

This is likely to with with alias / tuple things that happen in ast shakedown - or more specifically - have not happened due to the lack of other expressions. This will either be really simple to fix or a right pain, probably the latter :)

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fixed e4d4587