fix memory leak when handling background attribute (patch 1687900) [backport from HEAD]

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@45122 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/html/m_layout.cpp

@@ -352,6 +352,8 @@ TAG_HANDLER_BEGIN(BODY, "BODY")
                         winIface->SetHTMLBackgroundImage(image);
 #endif
                 }
+
+                delete fileBgImage;
             }
         }