Fixes shrinking shapes with gradients when the VirtualDev is
reused to create a alpha mask (and the texture is reused and
reading back from just one part of the texture which uses
glReadPixels code-path).

Binding texture is not necessary when we use and bind it to the
framebuffer.

Change-Id: Ie3994f749e1a2c17d4d3df44710b7453d7a4f45f