Handle empty mediaItems in search_album.

[JendaPlhak]

When I apply the media search_album function on one of my google photo albums, I get

  File "/home/asd/.local/lib/python3.8/site-packages/gphotospy/media.py", line 959, in search_album
    for media in curr_list:
TypeError: 'NoneType' object is not iterable

For some reason one of the media items responses is empty despite the fact that nextPageToken is not None and there is still at least one page left to be iterated. This fixes the problem.

[SmartManoj]

#19