GadtC with no constructors

Steps to reproduce

> :set -XTemplateHaskell -XGADTs
> $(pure [Language.Haskell.TH.DataD [] (Language.Haskell.TH.mkName "D") [] Nothing [Language.Haskell.TH.GadtC [] [] (Language.Haskell.TH.ConT (Language.Haskell.TH.mkName "D"))] []]);
*** Exception: compiler/typecheck/TcTyClsDecls.hs:2763:14-41: Non-exhaustive patterns in (dL -> L _ name) : _

Expected behavior

Probably a more welcoming error message.

Environment

GHC version used: GHC 8.6.5, GHC HEAD

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