tvplanit: Fix operation of navigation buttons in Preview dialog for weekview.

git-svn-id: https://svn.code.sf.net/p/lazarus-ccr/svn@8533 8e941d3f-bd1b-0410-a28a-d453659cc2b4

components/tvplanit/source/vpprtprv.pas

@@ -1112,6 +1112,7 @@ begin
   if v <> FZoomFactor then begin
     FZoomFactor := v;
     ClearPageData;
+    GeneratePageImage;
     SetScrollBars;
     Invalidate;
   end;