Specify correct size for disabled image list in wxMSW wxToolBar.

Specify correct size for disabled image list in wxMSW wxToolBar.

Use the real bitmap size instead of the default tool size when creating the
disabled image list as the actual bitmap size could be less than the default
one and in this case adding images to the image list later would fail (as
could be seen by using custom bitmaps in the toolbar sample).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67044 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775