Fix for Russian 7th mission, Seelow Hights

[Feh]

If you have trouble with this mission randomly failing in the stealth part, edit the mission.scn file in your save game and reset the corpse_count variable in the vars section. You get a waning at 43, and fail at 50. The variable gets incremented whenever a German sees another dead German. This can go up pretty fast because of the Russian AI "infiltration" on the left flank which calls artillery on the German line, pretty much wiping them out. Also, the Germans mount their own infiltration on right flank, and get wiped out again; ironically, this seems to be triggered by 20 bodies. I failed the counter without killing anyone with the guys I control. This mission obviously needed more QA before shipping.