amend problem with TextWindow.getStartLineBefore, where we were not following rule mentioned in previous commits to not count (graphical-chr -> \n) as line break

fcore/app-update.sml

@@ -262,34 +262,34 @@ struct
          let
           (* delete char at cursor and then decrement cursorIdx by 1
            * if cursorIdx is not 0 *)
-           val newBuffer = LineGap.delete (cursorIdx, 1, buffer)
+           val buffer = LineGap.delete (cursorIdx, 1, buffer)
            val cursorIdx = 
-             if Cursor.isPrevChrStartOfLine (newBuffer, cursorIdx)
+             if Cursor.isPrevChrStartOfLine (buffer, cursorIdx)
              orelse cursorIdx = 0 then
                cursorIdx
              else cursorIdx - 1
 
-           val newBuffer = LineGap.goToLine (startLine, newBuffer)
+           val buffer = LineGap.goToLine (startLine, buffer)
            val newApp = AppWith.bufferAndCursorIdx
-             (app, newBuffer, cursorIdx, NORMAL_MODE "", startLine)
+             (app, buffer, cursorIdx, NORMAL_MODE "", startLine)
 
            val drawMsg = 
              TextBuilder.build
-               (startLine, cursorIdx, newBuffer, windowWidth, windowHeight)
+               (startLine, cursorIdx, buffer, windowWidth, windowHeight)
          in
            (newApp, drawMsg)
          end
       else
         let
-          val newBuffer = LineGap.delete (cursorIdx, 1, buffer)
+          val buffer = LineGap.delete (cursorIdx, 1, buffer)
 
-          val newBuffer = LineGap.goToLine (startLine, newBuffer)
+          val buffer = LineGap.goToLine (startLine, buffer)
           val newApp = AppWith.bufferAndCursorIdx
-            (app, newBuffer, cursorIdx, NORMAL_MODE "", startLine)
+            (app, buffer, cursorIdx, NORMAL_MODE "", startLine)
 
           val drawMsg = 
             TextBuilder.build
-              (startLine, cursorIdx, newBuffer, windowWidth, windowHeight)
+              (startLine, cursorIdx, buffer, windowWidth, windowHeight)
       in
         (newApp, drawMsg)
       end

fcore/text-window.sml

@@ -20,23 +20,24 @@ struct
       | [] =>
           0
     else
-      let
-        val chr = String.sub (shd, sIdx)
-      in
-        if chr = #"\n" then
-          if absIdx <> cursorIdx then
-            getStartLineBefore
-              (sIdx - 1, shd, lineNum - 1, absIdx - 1, cursorIdx, stl)
+      if absIdx <= cursorIdx then
+        lineNum
+      else
+        let
+          val chr = String.sub (shd, sIdx)
+        in
+          if chr = #"\n" then
+            if isPrevChrLn (shd, sIdx, stl) then
+              (* \n -> \n *)
+              getStartLineBefore
+                (sIdx - 1, shd, lineNum - 1, absIdx - 1, cursorIdx, stl)
+            else
+              (* graphical-chr -> \n *)
+              getStartLineBefore
+                (sIdx - 1, shd, lineNum, absIdx - 1, cursorIdx, stl)
           else
-            (* we have found cursor, and it is at \n *)
-            lineNum - 1
-        else
-          if absIdx <> cursorIdx then
             getStartLineBefore
               (sIdx - 1, shd, lineNum, absIdx - 1, cursorIdx, stl)
-          else
-            (* we have found cursor; return line *)
-            lineNum - 1
       end
 
   fun getStartLineAfter