bug: single-state machine in infinite loop crashes after a while

[ghost]

bug

A finite state machine implemented using mruby-fsm with a single state in an infinite loop crashes after a random number of cycles.

how to reproduce

1. build mruby using "run_test.rb" provided in the repository;
2. run the following test program ("test.rb"):

fsm = FSM::Machine.new(:counter)
fsm.params.counter = 0

loop_state = FSM::State.new("loop")
loop_state.in_loop do
  fsm.params.counter += 1
  puts "fsm.params.counter += 1  =>  #{fsm.params.counter}"
end
loop_state.timing = 0.010
fsm.add(loop_state)

fsm.run "loop"

3. wait a random number of cycles (187|1006|6630|50826|73511|...) until the program exits with one of the following errors:

trace:
    [0] test.rb:12
test.rb:12: cannot set instance variable (ArgumentError)

or

trace:
    [0] test.rb:12
test.rb:12: non float value (TypeError)