Fix uploading gifs

Thom Wiggers
2018-03-20T17:34:35+01:00

Closes #610

#### Previous behaviour
Steps to reproduce:

1. upload GIF avatar or photo
2. OSError exception about the image conversion

#### New behaviour
Steps to validate that it works:

1. upload GIF avatar or photo
2. observe it wo...

Closes #610 (closed)

Previous behaviour

Steps to reproduce:

1. upload GIF avatar or photo

2. OSError exception about the image conversion

New behaviour

Steps to validate that it works:

1. upload GIF avatar or photo

2. observe it works.