mv_machine_learning: bug fix for invalid memory access

mv_machine_learning: bug fix for invalid memory access

[Issue type] bug fix

In the result() function of LandmarkDetection, ObjectDetection
and ObjectDetection3d task groups, the _result struct
was being cleared using memset to set all bytes to 0.
However, the structs include some vectors so this approach
of clearing the struct becomes invalid and resulted in
invalid memory access.

Change-Id: I98ed3e427e77b276145adbf461b3eaca44c752f6
Signed-off-by: Vibhav Aggarwal <v.aggarwal@samsung.com>