Set a default value for user stats to prevent error in scenario where the user has no stats

[madsbacha]

Set a default value for user stats to prevent error in scenario where the user has no stats.

In some scenarios, the stats object on the user looks like this:

"stats": {
  "diffStats": {
    "total": 0,
    "easy": 0,
    "normal": 0,
    "hard": 0,
    "expert": 0,
    "expertPlus": 0
  }
},

To fix the issue, we want to set a default value for these parameters to prevent the mod from throwing the error ".stats.totalUpvotes not found error"

Fixes #20

[FrozenAlex]

Looks good to me. Thank you for your contribution!