fix 'Cursor.getLineStartIdx' function, which should look at the left nodes if there is no relevant line in this node

fcore/cursor.sml

@@ -1125,14 +1125,37 @@ struct
   (* Prerequisite: move lineGap to reqLine *)
   fun getLineStartIdx (lineGap: LineGap.t, reqLine) =
     let
-      val {rightStrings, rightLines, line = bufferLine, idx = bufferIdx, ...} =
-        lineGap
+      val
+        { rightStrings
+        , rightLines
+        , line = bufferLine
+        , idx = bufferIdx
+        , leftStrings
+        , leftLines
+        , ...
+        } = lineGap
     in
       case (rightStrings, rightLines) of
         (shd :: stl, lhd :: ltl) =>
           (* reqLine exists in lineGap, so retrieve it *)
           let
             val relativeLine = reqLine - bufferLine - 1
+          in
+            if relativeLine < 0 then
+              (* line is in left node, if it exists *)
+              (case (leftStrings, leftLines) of
+                 (leftShd :: leftStl, leftLhd :: leftLtl) =>
+                   startVi0
+                     ( String.size leftShd - 1
+                     , leftShd
+                     , leftLhd
+                     , bufferIdx - 1
+                     , leftStl
+                     , leftLtl
+                     ) + 1
+               | (_, _) => 0)
+            else
+              let
                 val lineIdx = Vector.sub (lhd, relativeLine)
               in
                 if lineIdx = String.size shd - 1 andalso List.null stl then
@@ -1142,6 +1165,7 @@ struct
                 else
                   bufferIdx + lineIdx + 1
               end
+          end
       | (_, _) =>
           (* reqLine does not exist in lineGap, so just go to start of last line *)
           let

fcore/normal-mode/normal-mode.sml

@@ -192,7 +192,7 @@ struct
          * interpret as "go to line" command;
          * else, interpret as a command to move to end *)
         if String.size str = 0 then NormalMove.moveToEnd app
-        else NormalMove.moveToLine (app, count - 1)
+        else NormalMove.moveToLine (app, count)
     | #"%" => NormalMove.moveToMatchingPair app
     | #"x" => NormalDelete.removeChr (app, count, time)
     | #"J" => NormalDelete.removeLineBreaks (app, count, time)

fcore/normal-mode/normal-move.sml

@@ -107,6 +107,9 @@ struct
     end
 
   fun moveToLine (app: app_type, reqLine) =
+    let
+      val reqLine = reqLine - 1
+    in
       if reqLine = 0 then
         moveToStart app
       else
@@ -166,6 +169,7 @@ struct
             , visualScrollColumn
             )
         end
+    end
 
   fun moveToMatchingPair (app: app_type) =
     let