DiD S8: Disallow undead bat from retrieving the Book.

Resolves #7485.

(cherry picked from commit e917bf98e6)

data/campaigns/Descent_Into_Darkness/scenarios/08_Alone_at_Last.cfg

@@ -949,6 +949,10 @@
             [not]
                 type_adv_tree=Ghost,Vampire Bat
             [/not]
+            [not]
+                type_adv_tree=Walking Corpse
+                variation=bat
+            [/not]
             [not]
                 # this unit does not advance normally so each type has to be listed individually
                 type=Spectral Servant,Phantom,Eidolon
@@ -1033,6 +1037,28 @@
         [/message]
     [/event]
 
+    [event]
+        name=moveto
+        first_time_only=no
+        [filter]
+            x=$bookX
+            y=$bookY
+            side=1
+            type_adv_tree=Walking Corpse
+            variation=bat
+        [/filter]
+
+        [message]
+            speaker=unit
+            message= _ "..."
+        [/message]
+
+        [message]
+            speaker=Malin Keshar
+            message= _ "It’s impossible for a bat to carry a book that heavy."
+        [/message]
+    [/event]
+
     [event]
         name=time over