When invalidating default attributes, the mask to invalidate was set as
the current dirty mask, but it should have been or'ed with it.

The following test triggered a validation error on Linux:

dEQP.GLES2/functional_default_vertex_attrib_mat4_vertex_attrib_4fv

In this test, Vertex Array Bindings and Program dirty bits would set the
default attrib dirty mask to all the default attributes, but the
handling of Current Values dirty bits would mistakenly remove some of
those dirty bits.

Bug: angleproject:2786
Change-Id: Ife96621da7646102c1ce3b24e45f405e34a08b40
Reviewed-on: https://chromium-review.googlesource.com/c/1366797Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>