Rename misnamed lastGatheredType in ResourceGatherer.
Since it stores not the last gathered, but the last tasked type.
As discussed on IRC (http://irclogs.wildfiregames.com/%230ad-dev/2021-09-16-QuakeNet-%230ad-dev.log).
Differential revision: https://code.wildfiregames.com/D4277
Reviewed by: @bb
Comments by: @Angen, @Stan, @wraitii