Add wxUSE_TREELISTCTRL checks to treelist.cpp itself.

The contents of this file was still compiled even when wxUSE_TREELISTCTRL was
turned off. Fix this by adding the missing "#if wxUSE_TREELISTCTRL" check
around it.

Closes #13470.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69111 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/treelist.cpp

@@ -23,6 +23,8 @@
     #pragma hdrstop
 #endif
 
+#if wxUSE_TREELISTCTRL
+
 #ifndef WX_PRECOMP
     #include "wx/dc.h"
 #endif // WX_PRECOMP
@@ -1563,3 +1565,5 @@ wxDEFINE_TREELIST_EVENT(ITEM_ACTIVATED);
 wxDEFINE_TREELIST_EVENT(ITEM_CONTEXT_MENU);
 
 #undef wxDEFINE_TREELIST_EVENT
+
+#endif // wxUSE_TREELISTCTRL