glsl: don't generate extra errors in ValidateProgramPipeline

From Section 11.1.3.11 (Validation) of the GLES 3.1 spec:

   "An INVALID_OPERATION error is generated by any command that trans-
   fers vertices to the GL or launches compute work if the current set
   of active program objects cannot be executed, for reasons including:"

It then goes on to list the rules we validate in the
_mesa_validate_program_pipeline() function.

For ValidateProgramPipeline the only mention of generating an error is:

   "An INVALID_OPERATION error is generated if pipeline is not a name re-
   turned from a previous call to GenProgramPipelines or if such a name has
   since been deleted by DeleteProgramPipelines,"

Which we handle separately.

This fixes:
ES31-CTS.sepshaderobjs.PipelineApi

No regressions on the eEQP 3.1 tests.

Cc: Gregory Hainaut <gregory.hainaut@gmail.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>

src/mesa/main/pipelineobj.c

@@ -928,8 +928,11 @@ _mesa_ValidateProgramPipeline(GLuint pipeline)
       return;
    }
 
-   _mesa_validate_program_pipeline(ctx, pipe,
-                                   (ctx->_Shader->Name == pipe->Name));
+   /* ValidateProgramPipeline should not throw errors when pipeline validation
+    * fails and should instead only update the validation status. We pass
+    * false for IsBound to avoid an error being thrown.
+    */
+   _mesa_validate_program_pipeline(ctx, pipe, false);
 
    /* Validate inputs against outputs, this cannot be done during linking
     * since programs have been linked separately from each other.