load_followers_data(...) crashes on month change (upstream #3874)

[bugre]

I'm playing with InstaPy trying to understand IG user behavior. But for now, i was only tracking my followers and unfollowers on a daily basis (sometimes two or tree times, if i saw some bigger relation change.

I started around mid January, and on February, 1st the docker_quickstart.py that i was using started to crash on the "session.pick_unfollowers(...)" call.

My call is:
all_unfollowers, active_unfollowers = bot.pick_unfollowers(username="ig_id", compare_by="earliest", compare_track="first", live_match=True, store_locally=True, print_out=True)

I've checked if no corrupted json or something strange was present in the "~/InstaPy/logs/<my_id>/relationship_data/<ig_id>/followers" , and found nothing wrong with the data present there.

If you can create and assign the issue to me, i'll provide a suggested solution as soon i've it tested.

Expected Behavior

Collect and store follower/unfollower information.

Current Behavior

Crashing to collect unfollower users after month changed from January to February.
Crash occurs at: https://github.com/timgrossmann/InstaPy/blob/0c8a86057aa2959af47a38bca4f1c25edf92a1cd/instapy/relationship_tools.py#L1088

Possible Solution (optional)

I think i already found the problem ( as it crashes trying to "check" for a dictionary entry of the new month before setting it), and i'm currently testing a solution. I can provide a PR with it as soon i've done some more testing.

InstaPy configuration

Currently running the docker version, but problem is reproducible, with a very simple setup.

To reproduce the problem:

cd *directory where InstaPy is installed*
mkdir -p "logs/my_id/relationship_data/my_id/followers/"

touch '01-02-2019~full~11.json'
touch '30-01-2019~full~11.json'
touch '31-01-2019~full~11.json'

Then create a docker_quickstart.py with:

---

from instapy import InstaPy

bot = InstaPy(username='my_id', password='pass',
              selenium_local_session=False)

#get the unfollowers since beggining
all_unfollowers, active_unfollowers = bot.pick_unfollowers(username="my_id", compare_by="earliest", compare_track="first", live_match=True, store_locally=True, print_out=True)
bot.end()

---

*Crash traceback

web_1       | ___________________________________________________________________________
web_1       | INFO [2019-02-02 12:48:08] [my_id]  Starting to pick Unfollowers of my_id..
web_1       | """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
web_1       | Traceback (most recent call last):
web_1       |   File "code/docker_quickstart.py", line 7, in <module>
web_1       |     all_unfollowers, active_unfollowers = bot.pick_unfollowers(username="my_id", compare_by="earliest", compare_track="first", live_match=True, store_locally=True, print_out=True)
web_1       |   File "/code/instapy/instapy.py", line 3906, in pick_unfollowers
web_1       |     self.logfolder)
web_1       |   File "/code/instapy/relationship_tools.py", line 566, in get_unfollowers
web_1       |     logfolder)
web_1       |   File "/code/instapy/relationship_tools.py", line 1080, in load_followers_data
web_1       |     structured_entries["years"][entry_year]["months"][entry_month][
web_1       | KeyError: '02'
instapy_web_1 exited with code 1