Initialize ImplCursorData members as required

mbCurVisible is immediately read in ImplPrepForDraw, which inits some more
members but not mnStyle which is then read in ImplCursorInvert.  Regression
introduced with b9c10ee9 "weld
ClassificationDialog", found when valgrind'ing UITest_classification.

Change-Id: I986af0531e250953b8e45c914997b31c53a9ba91
Reviewed-on: https://gerrit.libreoffice.org/70876
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

vcl/source/window/cursor.cxx

@@ -163,6 +163,8 @@ void vcl::Cursor::ImplDraw()
 void vcl::Cursor::DrawToDevice(OutputDevice& rRenderContext)
 {
     ImplCursorData aData;
+    aData.mnStyle = 0;
+    aData.mbCurVisible = false;
     // calculate output area
     if (ImplPrepForDraw(&rRenderContext, aData))
     {