not checking mail folder sync error when LIST command's result callback is called.

not checking mail folder sync error when LIST command's result callback is called.

[Problem] the mails of INBOX was removed suddendly.
[Cause & Measure] Cause: mail folder sync operation is operated quite often.
But if there is a unexpected error in the folder sync time, we are guessing that not synced folder yet (because of network error) may be removed on mail server. so we are removing it from local db.

Change-Id: I33c2af6afd2956cfd188d5d0f6fc2df0dbb0ddaa
Signed-off-by: intae, jeon <intae.jeon@samsung.com>