[FeatureRequest] Handle map download with multiple instances.

[BiatuAutMiahn]

Using Nucleus CoOp, attempting to play with more than 1 instance. All players log in, and go to join game lobby.

Scenario 1:
Nobody has the map. Everyone is prompted to download the map. Map is downloaded then fails due to file being locked by another instance.

Scenario 2:
Nobody has map. Instance 1 downloads map. All other instances prompt for download as they do not check for maps except for on init.

Scenario 3:
Map exists in custom maps dir. All is good,

And a few proposed solutions:

1:

if (instanceNumber) {
    while (peer_count_with_map_status_downloading) {
        ReloadAllMaps();
        // wait 1000ms
    }
    // Return true for map being downloaded.
}

2:
if instanceNumber==0, and isMultiInstance: download map to .part file instead of .map, wait for peer_count_with_map_status_downloading==0.
with instanceNumber>0 wait for .part to not exist. then return true for download complete.

3:
postfix custom_maps_folder_path with instance number before download if isMultiInstance, instanceNumber>0, and map does not exist in custom_maps_folder_path.