Fix file selector crash

Sometimes a var change event came in while the file selector was
being rendered. Changes to the mFolderList or mFileList vectors
sometimes resulted in a crash. This patch set moves the
GetFileList call to the Render function to prevent the vectors
from changing while the render is taking place.
diff --git a/gui/objects.hpp b/gui/objects.hpp
index 8e0cc94..3a39fe5 100644
--- a/gui/objects.hpp
+++ b/gui/objects.hpp
@@ -495,6 +495,7 @@
 	COLOR mHighlightColor;
 	COLOR mFontHighlightColor;
 	int startSelection;
+	bool updateFileList;
 };
 
 class GUIListBox : public RenderObject, public ActionObject