Fix layouting of texture preview in atlas

Commit fe192fe58f added one extra level,
so we have to layout the parent of the parent now to actually layout the
sidebar.

Fixes: #8388
Signed-off-by: Ralph Sennhauser <ralph.sennhauser@gmail.com>

source/tools/atlas/AtlasUI/ScenarioEditor/Sections/Terrain/Terrain.cpp

@@ -168,7 +168,7 @@ public:
 			m_Sizer->Add(label, wxSizerFlags().Expand());
 
 			// We have to force the sidebar to layout manually
-			GetParent()->Layout();
+			GetParent()->GetParent()->Layout();
 
 			if (preview.loaded && m_Timer.IsRunning())
 			{