Summary:
To ensure initialize all fields of Ecore_Event_Mouse_XXX,
use calloc() instead of malloc().
Test Plan: N/A
Reviewers: gwanglim, cedric, raster, devilhorns, ManMower, zmike
Subscribers: jpeg, input.hacker, JHyun
Differential Revision: https://phab.enlightenment.org/D3906
Some fields (eg. data) may not be properly initialized.
Use calloc() instead of malloc() will ensure proper initialization
even if we add more fields.
These fields (data) would even be passed down to Evas as
Evas_Event_Key_Down for instance.