Don't try to use an undefined transition list

src/fsm.js

@@ -95,9 +95,11 @@ export function openAutomaton(name, states, editable = false) {
     for (const s of state) {
       if (s in states) {
         const transitions = states[s].transitions[letter];
+        if (transitions) {
           newStates.push(...transitions);
         }
       }
+    }
     state = newStates;
     updateUIState();
   }