DiD S9: increase health

Bats deal 3 damage.
Malin heals also 3 damage if he hits (unless the enemy has less than 6 health)
With 28 hp, Malin can take 9 more hits than he does,
compared to 6 previously on hard (and 8 previously on normal)

closes #5296

data/campaigns/Descent_Into_Darkness/scenarios/09_Descent_into_Darkness.cfg

@@ -1685,14 +1685,10 @@
         [unit]
             side=1
             x,y=3,34
-#ifdef HARD
-            hitpoints=22
-#endif
-#ifdef NORMAL
-            hitpoints=27
-#endif
 #ifdef EASY
             hitpoints=33
+#else
+            hitpoints=28
 #endif
             facing=se
             animate=yes