when downloading attachment automatically, mail body does not have to be downloaded...

when downloading attachment automatically, mail body does not have to be downloaded fully

[Problem] auto download attachment was not operated well.
[Cause & Measure] Cause: mail body was being downloaded fully to get attachment information completely before downloading attachment.
Measure: attachment information have to exist unconditionally if email size is "Header only"

Change-Id: Ic3b9c745b2b40a2631a43fd30535aed0f1f65ad5
Signed-off-by: intae, jeon <intae.jeon@samsung.com>
(cherry picked from commit eb2b71afca503c9a390d0b7d50647f4ea552e372)