When printing with external spool holder (no AMS connected), the printer
reported error [0700-8012] "Failed to get AMS mapping table".
Root cause: The ams_mapping2 calculation for external spool (tray_id=254)
was incorrectly computing ams_id=63, slot_id=2 instead of the required
ams_id=255, slot_id=254.
The fix adds special handling for external spool tray IDs (254 for main
nozzle, 255 for deputy nozzle) which use ams_id=255 with slot_id matching
the tray_id.
Fixes#213
maziggy
60bb29be2f