Runtime crash with bogus score entry

[jabdoa2]

MPF crashes during runtime. We should either refuse a broken score entry on boot/validate or it should work.

DEBUG : Events : ============== EVENTS QUEUE =============
DEBUG : Events : sw_playfield_active, None, None, {}
DEBUG : Events : s_stage_target_inactive, None, None, {}
DEBUG : Events : player_stage_jackpot, None, None, {'change': 1000, 'player_num': 1, 'value': 1100, 'prev_value': 100}
DEBUG : Events : mode_stage_stage_jackpot_score, None, None, {'change': 0, 'value': 1000, 'prev_value': 1000}
DEBUG : Events : =========================================
ERROR : root : need more than 1 value to unpack
Traceback (most recent call last):
 File "/home/pi/mpf/mpf/commands/core.py", line 133, in __init__
   MachineController(mpf_path, machine_path, vars(args)).run()
 File "/home/pi/mpf/mpf/core/machine.py", line 544, in run
   self._run_loop()
 File "/home/pi/mpf/mpf/core/machine.py", line 565, in _run_loop
   self.process_frame()
 File "/home/pi/mpf/mpf/core/machine.py", line 580, in process_frame
   self.events.process_event_queue()
 File "/home/pi/mpf/mpf/core/events.py", line 477, in process_event_queue
   **event[3])
 File "/home/pi/mpf/mpf/core/events.py", line 412, in _process_event
   result = handler[0](**merged_kwargs)
 File "/home/pi/mpf/mpf/core/scoring.py", line 70, in _score_event_callback
   value, block = value.split('|')
ValueError: need more than 1 value to unpack