program_resource: subroutine active uniforms should return NumSubroutineUniforms

program_resource: subroutine active uniforms should return NumSubroutineUniforms

Before this commit, GetProgramInterfaceiv for pname ACTIVE_RESOURCES
and all the <shader>_SUBROUTINE_UNIFORM programInterface were
returning the count of resources on the shader program using that
interface, instead of the num of uniform resources. This would get a
wrong value (for example) if the shader has an array of subroutine
uniforms.

Note that this means that in order to get a proper value, the shader
needs to be linked, something that is not explicitly mentioned on
ARB_program_interface_query spec, but comes from the general
definition of active uniform. If the program is not linked we
return 0.

v2: don't generate an error if the program is not linked, returning 0
    active uniforms instead, plus extra spec references (Tapani Palli)

Fixes GL44-CTS.program_interface_query.subroutines-compute

Reviewed-by: Tapani Pälli <tapani.palli@intel.com>