Fix(VIM-3179): Respect virtual space below editor (imperfectly)

src/main/java/com/maddyhome/idea/vim/helper/EditorHelper.java

@@ -342,7 +342,7 @@ public class EditorHelper {
 
     final int offset = y - ((screenHeight - lineHeight) / lineHeight / 2 * lineHeight);
     final @NotNull VimEditor editor1 = new IjVimEditor(editor);
-    final int lastVisualLine = EngineEditorHelperKt.getVisualLineCount(editor1) - 1;
+    final int lastVisualLine = EngineEditorHelperKt.getVisualLineCount(editor1) + editor.getSettings().getAdditionalLinesCount();
     final int offsetForLastLineAtBottom = getOffsetToScrollVisualLineToBottomOfScreen(editor, lastVisualLine);
 
     // For `zz`, we want to use virtual space and move any line, including the last one, to the middle of the screen.

src/main/java/com/maddyhome/idea/vim/helper/ScrollViewHelper.kt

@@ -59,7 +59,7 @@ internal object ScrollViewHelper {
     // that this needs to be replaced as a more or less dumb line for line rewrite.
     val topLine = getVisualLineAtTopOfScreen(editor)
     val bottomLine = getVisualLineAtBottomOfScreen(editor)
-    val lastLine = vimEditor.getVisualLineCount() - 1
+    val lastLine = vimEditor.getVisualLineCount() + editor.settings.additionalLinesCount
 
     // We need the non-normalised value here, so we can handle cases such as so=999 to keep the current line centred
     val scrollOffset = injector.options(vimEditor).scrolloff