Fix for issue #1234: Access violation while changing the theme

Demos/Advanced/Advanced.dsv

@@ -0,0 +1,10 @@
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xTb3VyY2VcVmlydHVhbFRyZWVzLnBhcw==]
+Module=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+CursorX=42
+CursorY=667
+TopLine=611
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+

Demos/Interfaces/charityevents.dsv

@@ -0,0 +1,30 @@
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xTb3VyY2VcVmlydHVhbFRyZWVzLnBhcw==]
+Module=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+CursorX=47
+CursorY=246
+TopLine=223
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xEZW1vc1xJbnRlcmZhY2VzXG15ZXZlbnRzLnBh
+cw==]
+Module=D:\Projects\Virtual-TreeView\Demos\Interfaces\myevents.pas
+CursorX=6
+CursorY=26
+TopLine=13
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Demos\Interfaces\myevents.pas
+
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xEZW1vc1xPYmplY3RzXE1WQ1BhbmVsLnBhcw==]
+Module=D:\Projects\Virtual-TreeView\Demos\Objects\MVCPanel.pas
+CursorX=21
+CursorY=74
+TopLine=52
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Demos\Objects\MVCPanel.pas
+

Demos/Minimal/Minimal.dsv

@@ -0,0 +1,20 @@
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xTb3VyY2VcVmlydHVhbFRyZWVzLnBhcw==]
+Module=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+CursorX=42
+CursorY=667
+TopLine=626
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xEZW1vc1xNaW5pbWFsXE1haW4ucGFz]
+Module=D:\Projects\Virtual-TreeView\Demos\Minimal\Main.pas
+CursorX=1
+CursorY=1
+TopLine=1
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=
+

Demos/OLE/OLE.dsv

@@ -0,0 +1,10 @@
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xEZW1vc1xPTEVcTWFpbi5wYXM=]
+Module=D:\Projects\Virtual-TreeView\Demos\OLE\Main.pas
+CursorX=1
+CursorY=1
+TopLine=1
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=
+

Demos/Objects/MVCDemo.dsv

@@ -0,0 +1,10 @@
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xTb3VyY2VcVmlydHVhbFRyZWVzLnBhcw==]
+Module=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+CursorX=42
+CursorY=667
+TopLine=626
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+

Packages/RAD Studio 10.4+/VirtualTreesR.dsv

@@ -0,0 +1,20 @@
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xTb3VyY2VcVmlydHVhbFRyZWVzLnBhcw==]
+Module=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+CursorX=42
+CursorY=667
+TopLine=626
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xEZW1vc1xPYmplY3RzXE1WQ1R5cGVzLnBhcw==]
+Module=D:\Projects\Virtual-TreeView\Demos\Objects\MVCTypes.pas
+CursorX=36
+CursorY=194
+TopLine=172
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Demos\Objects\MVCTypes.pas
+

Source/VirtualTrees.StyleHooks.pas

@@ -523,10 +523,16 @@ procedure TVclStyleScrollBarsHook.WMCaptureChanged(var Msg: TMessage);
 
 destructor TVclStyleScrollBarsHook.Destroy;
 begin
-  FVertScrollWnd.StyleHook := nil;
-  FreeAndNil(FVertScrollWnd);
-  FHorzScrollWnd.StyleHook := nil;
-  FreeAndNil(FHorzScrollWnd);
+  if Assigned(FVertScrollWnd) then
+  begin
+    FVertScrollWnd.StyleHook := nil;
+    FreeAndNil(FVertScrollWnd);
+  end;
+  if Assigned(FHorzScrollWnd) then
+  begin
+    FHorzScrollWnd.StyleHook := nil;
+    FreeAndNil(FHorzScrollWnd);
+  end;
   inherited;
 end;