Coop replays missing mapname in the replay file

When opening the replay files I found out that the coop replays are missing the mapname. The client is then not showing them properly in the online vault, and downlord's client can't even lauch the replays.

I dont know if it would completelly fix the issue with coop replays, but it would surely be a good start.

Some examples of the replays files:
Coop Game:
```
{"num_players": 1, "featured_mod_versions": {"1": 55, "2": 55, "3": 49, "4": 49, "5": 49, "6": 49, "7": 51, "8": 49, "9": 50, "10": 50, "11": 50, "12": 50, "13": 50, "14": 50, "15": 49, "16": 49, "17": 50, "18": 51, "19": 50, "20": 50, "21": 51, "22": 49}, "game_end": 1544305811.890091, "uid": 8945286, "title": "Wastefield's game", "game_type": 3, "teams": {}, "mapname": "", "featured_mod": "coop", "complete": true}
```
`"mapname": ""`

FAF game
```
{"num_players": 2, "featured_mod_versions": {}, "game_end": 1544306269.963174, "uid": 8945278, "title": "FaReNoy Vs bisq01", "game_type": 0, "teams": {"1": ["FaReNoy"]}, "mapname": "x1mp_017", "host": "FaReNoy", "featured_mod": "ladder1v1", "complete": true}
```
`"mapname": "x1mp_017"`