evas image: fix non-rendered preload image.

evas image: fix non-rendered preload image.

Summary:
This is one more corner-case issue that I found,
When second image doesn't use preload (but still share the resource)
canvas engine triggers cancellation for first image preload function.

Unluckly, preload thread is cancelled on the intermediate rendering,
First image is not going to rendered, even image turn it changed states.
Because end of that frame, canvas reset/flushed all active objects.

Here changes to retain the changes status to redraw it in the next frame.

Test Plan:
img1 = image_add;
image_file_set(img1, "test.jpg");
image_preload(img1, true);
show(img);

img2 = image_add;
image_file_set(img2, "test.jpg");  //same resource
image_preload(img2, false);
show(img2);

img1 is invisible.

Reviewers: #committers

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D7157

Change-Id: I3bdaee67d55424dc6385faa355d295f0c444e25a