GetPaths/GetFilenames() must be used instead when more than one file could be selected: document this and assert if the wrong functions are called. Closes https://github.com/wxWidgets/wxWidgets/pull/1883
GetPaths/GetFilenames() must be used instead when more than one file could be selected: document this and assert if the wrong functions are called. Closes https://github.com/wxWidgets/wxWidgets/pull/1883