mesa: return initial value for VALIDATE_STATUS if pipe not bound

mesa: return initial value for VALIDATE_STATUS if pipe not bound

From OpenGL 4.5 Core spec (7.13):

    "If pipeline is a name that has been generated (without subsequent
    deletion) by GenProgramPipelines, but refers to a program pipeline
    object that has not been previously bound, the GL first creates a
    new state vector in the same manner as when BindProgramPipeline
    creates a new program pipeline object."

I interpret this as "If GetProgramPipelineiv gets called without a
bound (but valid) pipeline object, the state should reflect initial
state of a new pipeline object." This is also expected behaviour by
ES31-CTS.sepshaderobjs.PipelineApi conformance test.

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Marta Lofstedt <marta.lofstedt@intel.com>