crash occured when downloading partial body

crash occured when downloading partial body

[Problem] crash occured when downloading partial body
[Cause & Measure] Cause:
1. email-service requested UID, BODYSTRUCTURE, BODY to server.
2. UID was comming wrongly as 0. (not reproduced..)
3. email-service iterated its partial body download events to find proper event by comparing UID but it couldn't.
4. the array of partial body download events was out of bound
Measure: Adjusting the bound of index in iteration.

Change-Id: I8fdfe6d827b98f471b56ce6fe7481681cffc3028
Signed-off-by: intae, jeon <intae.jeon@samsung.com>