fix "osv info threads" gdb command

If thread is not started its cpu pointer will be NULL. Handle this
case properly.

Signed-off-by: Gleb Natapov <gleb@cloudius-systems.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>

scripts/loader.py

@@ -748,7 +748,7 @@ class osv_info_threads(gdb.Command):
 
                 gdb.write('%4d (0x%x) %-15s cpu%s %-10s %s vruntime %12g\n' %
                           (tid, ulong(t), name,
-                           cpu['arch']['acpi_id'],
+                           cpu['arch']['acpi_id'] if cpu != 0 else "?",
                            thread_status(t),
                            location,
                            t['_runtime']['_Rtt'],