special case LineGap.goToLine, when the line requested to go to is 0. When this happens, we call 'LineGap.goToStart'.

src/line_gap.sml

@@ -3047,11 +3047,14 @@ struct
         , lineLength
         } = buffer
     in
+      if searchLine <= 0 then
+        LineGap.goToStart buffer
+      else
         (* we compare current line with searchLine - 1
          * because if searchLine - 1 is here,
          * that means we can access the linebreak 
          * that starts searchLine *)
-      if searchLine - 1 < line then
+        (if searchLine - 1 < line then
            helpGoToLineLeft
              ( idx
              , line
@@ -3076,7 +3079,7 @@ struct
              , lineLength
              )
          else
-        buffer
+           buffer)
     end
 
   fun helpGoToIdxLeft