Add support for loading old V1 bitmap files to wxBMPHandler.

Such files are apparently still seen in the wild, even though this format has
been superseded since Windows 3.0 (!).

Closes #3433.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76144 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775