Hotfix 2 for gyms

[goedzo]

Fixes:

[2017-07-23 16:45:09] [ cli] [INFO] Most Perfect Pokemon: Goldeen [CP: 388] [IV: 15/7/14] Potential: 0.8
Traceback (most recent call last):
File "pokecli.py", line 884, in
main()
File "pokecli.py", line 206, in main
bot.tick()
File "/usr/src/app/pokemongo_bot/init.py", line 834, in tick
if worker.work() == WorkerResult.RUNNING:
File "/usr/src/app/pokemongo_bot/cell_workers/gym_pokemon.py", line 156, in work
result = self.move_to_destination()
File "/usr/src/app/pokemongo_bot/cell_workers/gym_pokemon.py", line 322, in move_to_destination
self.drop_pokemon_in_gym(self.destination, current_pokemons)
File "/usr/src/app/pokemongo_bot/cell_workers/gym_pokemon.py", line 465, in drop_pokemon_in_gym
if not first_time:
UnboundLocalError: local variable 'first_time' referenced before assignment

[mention-bot]

@goedzo, thanks for your PR! By analyzing the history of the files in this pull request, we identified @davidakachaos to be a potential reviewer.