fixed mem leak

src/lcl/fresnel.lcl.pas

@@ -406,11 +406,15 @@ end;
 constructor TFresnelLCLWidgetSet.Create(AOwner: TComponent);
 begin
   inherited Create(AOwner);
+  if FresnelLCLWidgetSet<>nil then
+    raise Exception.Create('TFresnelLCLWidgetSet.Create');
+  FresnelLCLWidgetSet:=Self;
 end;
 
 destructor TFresnelLCLWidgetSet.Destroy;
 begin
   inherited Destroy;
+  FresnelLCLWidgetSet:=nil;
 end;
 
 procedure TFresnelLCLWidgetSet.AppProcessMessages;