fix very minor issue in cursor.sml's 'helpViL' function (previously returned cursorIdx when non-line breaks is followed by non-line break, but now return cursorIdx + 1 instead which is the correct behaviour, because we want to move the cursor rightwards one position in that case

fcore/cursor.sml

@@ -146,7 +146,7 @@ struct
               cursorIdx + 2
             else
               (* non-line break followed by non-line break *)
-              cursorIdx
+              cursorIdx + 1
         | [] => 
             cursorIdx)