hw/acpi: Fix GPtrArray memory leak in crs_range_merge

hw/acpi: Fix GPtrArray memory leak in crs_range_merge

This leak was detected by the valgrind.

The crs_range_merge() function unconditionally allocated a GPtrArray
'even when range->len was zero, causing an early return without freeing
the allocated array. This resulted in a memory leak when an empty range
was processed.

Instead of moving the allocation after the check (as previously attempted),
use g_autoptr for automatic cleanup. This ensures the array is freed even
on early returns, and also removes the need for the explicit free at the
end of the function.

Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Message-Id: <20250613085110.111204-1-lizhijian@fujitsu.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Ani Sinha <anisinha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>