evas gl: fix invalid image size.
When we reset of texture for a valid object,
this object cache size become -1 x -1 with null texture.
Later, we reset a new texture of the object,
Its texture size could be -1 x -1.
That brings to incorrect result drawing.
Can't see any points of using cache size there.
This bug was introduced by 9e01cf2698d5b24f440d696fd57d469cdc5a6b5f
Reviewers: committers, raster
Differential Revision: https://phab.enlightenment.org/D7077