Coverity issues bug fixes

:Detailed Notes:
Fixed uninitialized scalar field
  - include/internal/Callback.h
Fixed uninitialized pointer field
  - src/MojoCall.cpp
  - include/internal/MojoCall.h
Fixed unchecked return value
  - src/ActivityCategory.cpp
  - src/DevelCategory.cpp
  - src/TestCategory.cpp

:Testing Performed:
Compiled locally and tested on official build.

:QA Notes:

:Issues Addressed:
[GF-51356] Activity Manager : Fix Issue From Static Analysis (Coverity)

Open-webOS-DCO-1.0-Signed-off-by: heekwon kang <hk.kang@lge.com>

Change-Id: I069018626c4face88b989737bb39fb1d66faee99
Reviewed-on: https://g2g.palm.com/3905
Reviewed-by: Build Verification
Reviewed-by: Heekwon Kang <hk.kang@lge.com>
Tested-by: Heekwon Kang <hk.kang@lge.com>
Reviewed-by: Alan Levi <alan.levi@lge.com>