Allow undo move if not picking item or elixir

If we select the option to leave the item on the ground, we should be
able to undo and move another unit to take it.

data/campaigns/Eastern_Invasion/utils/items.cfg

@@ -66,6 +66,10 @@
                         [/modify_unit]
                         {EQUIP_WML}
                     [/then]
+                    [else]
+                        [allow_undo]
+                        [/allow_undo]
+                    [/else]
                 [/if]
             [/then]
 
@@ -1091,6 +1095,10 @@ plague_staff #enddef
                 [/remove_item]
                 {MODIFY}
             [/then]
+            [else]
+                [allow_undo]
+                [/allow_undo]
+            [/else]
         [/if]
     [/event]
 #enddef