Fix missing return value in CGUIButton::ButtonImage::operator=

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@4764 dfc29bdd-3216-0410-991c-e03cc46cb475

source/Irrlicht/CGUIButton.h

@@ -188,6 +188,7 @@ namespace gui
 					Texture->drop();
 				Texture = other.Texture;
 				SourceRect = other.SourceRect;
+				return *this;
 			}
 
 			bool operator==(const ButtonImage& other) const