Keep autoDistribute through sheet edits

Fixes #259

src/Handler/Sheet.hs

@@ -484,21 +484,22 @@ handleSheetEdit tid ssh csh msId template dbAction = do
       saveOkay <- runDB $ do
         actTime <- liftIO getCurrentTime
         cid <- getKeyBy404 $ TermSchoolCourseShort tid ssh csh
+        oldAutoDistribute <- fmap sheetAutoDistribute . join <$> traverse get msId
         let newSheet = Sheet
-              { sheetCourse       = cid
-              , sheetName         = sfName
-              , sheetDescription  = sfDescription
-              , sheetType         = sfType
-              , sheetGrouping     = sfGrouping
-              , sheetMarkingText  = sfMarkingText
-              , sheetVisibleFrom  = sfVisibleFrom
-              , sheetActiveFrom   = sfActiveFrom
-              , sheetActiveTo     = sfActiveTo
-              , sheetHintFrom     = sfHintFrom
-              , sheetSolutionFrom = sfSolutionFrom
-              , sheetUploadMode   = sfUploadMode
+              { sheetCourse         = cid
+              , sheetName           = sfName
+              , sheetDescription    = sfDescription
+              , sheetType           = sfType
+              , sheetGrouping       = sfGrouping
+              , sheetMarkingText    = sfMarkingText
+              , sheetVisibleFrom    = sfVisibleFrom
+              , sheetActiveFrom     = sfActiveFrom
+              , sheetActiveTo       = sfActiveTo
+              , sheetHintFrom       = sfHintFrom
+              , sheetSolutionFrom   = sfSolutionFrom
+              , sheetUploadMode     = sfUploadMode
               , sheetSubmissionMode = sfSubmissionMode
-              , sheetAutoDistribute = False
+              , sheetAutoDistribute = fromMaybe False oldAutoDistribute
               }
         mbsid <- dbAction newSheet
         case mbsid of