ControlImp::ResolveMap()'s so called "absolute path" section may actually take relative path

Inside ControlImp::ResolveMap() of sc2_client.cc:
```
// Absolute path
SC2APIProtocol::LocalMap* local_map = request->mutable_local_map();
if (DoesFileExist(map_name)) {
local_map->set_map_path(map_name);
return;
}
```

I can pass in a relative path that would pass the DoesFileExist check with proper VisualStudio "Working Directory" setting. But the relative path doesn't work when Starcraft game tries to open it (Maybe because it is working under another directory and communicate through network port?).

Anyway, I think ```map_name``` should probably be converted into absolute path before being assigned to ```local_map``` here.