evas filter: make curve work for every

evas filter: make curve work for every

Summary:
If an input buffer and an output buffer for the curve filter are same, it reads
and writes to the same texture which behavior is not defined. I could not find
good reference for this, but following could be a reference.

https://stackoverflow.com/questions/11410292/opengl-read-and-write-to-the-same-texture

The texture gets 0 color value as a result. So the curve filter does not work.
This patch makes the curve filter use different input and output buffer.

Test Plan:
This attached file could explain what 'read and write to the same texture' is.
{F3724537}

Reviewers: Hermet, jpeg, jsuya

Reviewed By: Hermet

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D9085