eet: read sould be failed if cipher_key exist but file not ciphered

eet: read sould be failed if cipher_key exist but file not ciphered

Summary:
Currentely, if eet_read_cipher()'s cipher_key param is exist but file
not ciphered, function always read and return successful result.
But, this behavior can not check data integrity.

e.g.
1. App create config file using eet with encryption key.
2. Attacker replace config to malicious config (not encryted).
3. App can not notice if eet_read_cipher() read that successfully.

@fix

Test Plan:
$eet -e test.cfg my_config test.src 1
$eet -d test.cfg my_config decode_res.txt my_encrytion_key

(Currentely decode success, but should be failed)

Reviewers: woohyun, raster

Subscribers: id213sin, akanad, cedric, jpeg

Differential Revision: https://phab.enlightenment.org/D4563

Signed-off-by: Cedric BAIL <cedric@osg.samsung.com>