mesa: in _mesa_combine_programs() take new STATE_CURRENT_ATTRIB color into account

Commit 1680ef869625dc1fe9cf481b180382a34e0738e7 changed the texenv program
to get color from a state register instead of a constant-valued vertex
attribute.  This broke program concatenation (so glDraw/CopyPixels broke).
Now check if the second program get's color from a constant register and
handle that case appropriately.
1 file changed