just in case. one more nil check

aaaand where it was actually crashing

Add nil checks on HHGear to rope steps.

issue #871 in hedgewars: "Hedgehog dropping into water while still attached to a rope makes engine crash" Due to doStepRopeWork's being completely skipped 75% of the ticks - including drowning/detachment-condition checks

add a couple of onGearDamage callbacks to mine/barrel fall damage

issue #867: Update German mission strings

small code tweak

fix for issue #855: Failure to teleport rarely makes engine crash

issue #829: Drill rocket drilling dust is slightly misplaced

issue #852: Using blowtorch to dig through the wrap-around border in caves fails miserably