Fix mine production resource limit for peffic != 100%

Fix mine production resource limit for peffic != 100%

With etu_per_update large and resource depletion quick, a sector can
produce more work than is required to fully deplete a mine.  In that
case, produce() and prod() limit production to what is actually in the
ground.  Except produce() got it wrong for sector types with
production efficiency other than 100%.

This affects mountains in the stock game, but only with impractically
large etu_per_update.