S3Boto3StorageFile close() should mimic FileSystemStorage.close() for empty files

[Masterdanielsan]

S3Boto3StorageFile close() vs. FileSystemStorage.close()
The following code will fail to write a file in the former case but not in the latter:

Setup: 'some/path/to/file.txt' doesn't exist in S3 or on File system in either case

file = default_storage.open('some/path/to/file.txt', 'w')
file.close()

One shouldn't have to call file.write() before file.close() in order to create an empty file.

This would make S3Boto3StorageFile consistent with a regular python open() command as well as the FileSystemStorage.open() command.