Fixed issue JAM-Software#458: If the Virtual TreeView control is plac…

…ed on a control that has the StyleEx flag WS_EX_COMPOSITED set, horizontal scrolloing does not update the header

# Conflicts:
#	Source/VirtualTrees.pas

Source/VirtualTrees.pas

@@ -18970,13 +18970,9 @@ procedure TBaseVirtualTree.WMNCPaint(var Message: TRealWMNCPaint);
     DC := GetDCEx(Handle, Message.Rgn, Flags or DCX_INTERSECTRGN);
 
   if DC <> 0 then
-  begin
-    if hoVisible in FHeader.FOptions then
-    begin
-      R := FHeaderRect;
-      FHeader.FColumns.PaintHeader(DC, R, -FEffectiveOffsetX);
-    end;
+  try
     OriginalWMNCPaint(DC);
+  finally
     ReleaseDC(Handle, DC);
   end;
     if tsUseThemes in FStates then
@@ -18986,7 +18982,8 @@ procedure TBaseVirtualTree.WMNCPaint(var Message: TRealWMNCPaint);
 //----------------------------------------------------------------------------------------------------------------------
 
 procedure TBaseVirtualTree.WMPaint(var Message: TWMPaint);
-
+var
+  DC: HDC;
 begin
   if tsVCLDragging in FStates then
     ImageList_DragShowNolock(False);
@@ -18999,6 +18996,17 @@ procedure TBaseVirtualTree.WMPaint(var Message: TWMPaint);
 
   if tsVCLDragging in FStates then
     ImageList_DragShowNolock(True);
+
+  if hoVisible in FHeader.FOptions then
+  begin
+    DC := GetDCEx(Handle, 0, DCX_CACHE or DCX_CLIPSIBLINGS or DCX_WINDOW or DCX_VALIDATE);
+    if DC <> 0 then
+      try
+        FHeader.FColumns.PaintHeader(DC, FHeaderRect, -FEffectiveOffsetX);
+    finally
+      ReleaseDC(Handle, DC);
+    end;
+  end;//if header visible
 end;
 
 //----------------------------------------------------------------------------------------------------------------------