Studio: forward --has-rocm from setup.sh when gfx resolution fails (#5927)

setup.ps1 already forwards --has-rocm whenever AMD is detected regardless
of whether gfx resolved. setup.sh only forwarded --rocm-gfx, so a Linux
host where AMD was detected but gfx resolution failed would forward nothing,
leaving the installer with has_rocm=False and falling back to a source build.

Add the elif branch to forward --has-rocm when _setup_amd_detected is true
but _setup_gfx is empty, matching setup.ps1 parity. Add a source-level test
to verify both flags are present in setup.sh.