fix: Astrid.Query.andThen compose with map*

Reserve stack slots for andThen values and fill them in later. The old
approach of a strict stack machine was wrong.

lib/sql/src/Astrid/Query.elm

@@ -1,6 +1,7 @@
 module Astrid.Query
     exposing
-        ( Query
+        ( Error
+        , Query
         , andThen
         , errorToString
         , execute
@@ -54,7 +55,7 @@ javascript.
 dummyExecute : Result Error a
 dummyExecute =
     let
-        query = Dummy
+        _ = Dummy
         _ = Execute "" ""
         _ = Decode "" 0 (Json.Decode.Failure "" Json.Encode.null)
         _ = Failure ""
@@ -96,5 +97,5 @@ map5 f a b c d e =
     Dummy
 
 andThen : (a -> Query b) -> Query a -> Query b
-andThen f a =
+andThen f q =
     Dummy