Check if the colour string is not empty before trying to pull something out of it.  See #15210.

git-svn-id: http://svn.wxwidgets.org/svn/wx/wxPython@74026 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
fixes for the dataview samples

git-svn-id: http://svn.wxwidgets.org/svn/wx/wxPython@74027 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775