Fix cursor invalidation, again (#17617)

Regressed in #15500, incorrectly fixed in #17332, exposed by #17583.
My ineptitude on full display. If this isn't the last cursor
invalidation bug I'm going to cry.

Closes #17615

## Validation Steps Performed
* cmd.exe
* a directory with 6 files
* 80x24 viewport
* run `cls`
* run `dir` twice

src/renderer/base/renderer.cpp

@@ -435,8 +435,9 @@ bool Renderer::_CheckViewportAndScroll()
         auto coordCursor = _currentCursorOptions.coordCursor;
 
         // `coordCursor` was stored in viewport-relative while `view` is in absolute coordinates.
-        // --> Turn it back into the absolute coordinates with the help of the old viewport.
-        coordCursor.y += srOldViewport.top;
+        // --> Turn it back into the absolute coordinates with the help of the viewport.
+        // We have to use the new viewport, because _ScrollPreviousSelection adjusts the cursor position to match the new one.
+        coordCursor.y += srNewViewport.top;
 
         // Note that we allow the X coordinate to be outside the left border by 1 position,
         // because the cursor could still be visible if the focused character is double width.