[Fixed]-Clean() method causes files to lose data using POST form

When you read the file content (for calculating md5 hash) you need to move the file object’s position to the beginning (0th byte) using file.seek:

md5hash = md5()
for chunk in f.chunks():
    md5hash.update(chunk)
file_hash = md5hash.hexdigest()
f.seek(0)  #<-- add this line