Summary:
1) According to description in .eo file,
some APIs return not 0 when the given object is NULL or not proper object.
But, several APIs are not implemented as those description.
Now, they will return a value as description.
2) If there is no description about the return value when the API fail,
put description according to pair API or old version of elementary.
@fix
Reviewers: woohyun, Hermet, seoz
Differential Revision: https://phab.enlightenment.org/D1933
Tom Hacohen
Youngbok Shin
Daniel Kolesa