Fix invalid trigger killing FSMBase

lib/tfw/fsm_base.py

@@ -3,7 +3,7 @@
 
 from collections import defaultdict
 
-from transitions import Machine
+from transitions import Machine, MachineError
 
 from tfw.mixins import CallbackMixin
 from tfw.config.logs import logging
@@ -61,5 +61,5 @@ class FSMBase(Machine, CallbackMixin):
         if all(predicate_results):
             try:
                 self.trigger(trigger)
-            except AttributeError:
+            except (AttributeError, MachineError):
                 LOG.debug('FSM failed to execute nonexistent trigger: "%s"', trigger)