Test for artist image. Fails.
Fix for https://github.com/alecksphillips/wallpaperfm/issues/3. Include type of chart in filename.
Fix artist bug (https://github.com/alecksphillips/wallpaperfm/issues/3). Some artists (eg Slamin' Gladys) have no images. For some other reason, the Python 2.x tests are limited to 71 top artists, and the 3.x to 80, and this imageless artist is at position 71.