efl-mono: Only raise exception for managed errors.

efl-mono: Only raise exception for managed errors.

Summary:
Previously, any unhandled Eina_Error would cause an exception
to be thrown when the control returned to C#.

This commit changes this behavior to only raise it when an exception
went unhandled from a C# callback back to C, like in an event handler,
for example.

Test Plan: run tests

Reviewers: segfaultxavi, Jaehyun_Cho, felipealmeida

Reviewed By: Jaehyun_Cho

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D7537