Crash occurred when "" is inputted as new mailbox name when creating or renaming...

Crash occurred when "" is inputted as new mailbox name when creating or renaming folder

[Model] Z2
[BinType] AP
[Customer] N/A
[Issue#] P160512-05930
[Request] PLM
[Occurrence Version] APE4
[Problem] Crash occurred when "" is inputted as new mailbox name when creating or renaming folder.
[Cause & Measure] Cause: There is null checking logic, but string length check does not exist.
Measure: Add strlen check logic.
[Checking Method] Trying to add or rename mail folder.
[Team] Email
[Developer] san.cho@samsung.com
[Solution company] Samsung
[Change Type] N/A
Change-Id: I7549dfecce93f8775ffca1f73086c94214f3ddd4
Signed-off-by: intae, jeon <intae.jeon@samsung.com>