HttT scenario 4: Use find_vacant=yes to unstore Delfador at the end

Fixes the somewhat unlikely situation of him clobbering whichever unit
happens to be standing on 31,11 and causing it to disappear from the
game forever (especially bad if it's a player unit).

This commit is dedicated to my loyal Knight Haldiel, who became victim
to this oversight.

changelog

@@ -1,4 +1,9 @@
 Version 1.11.9+dev:
+ * Campaigns:
+   * Heir to the Throne:
+     * Fixed Delfador clobbering whichever unit happens to be standing on
+       31,11 at the end of The Bay of Pearls, causing it to disappear
+       forever.
  * GUI2
    * Added: FAI-function handling in GUI2 widgets.
    * Added: A new tooltip window.

data/campaigns/Heir_To_The_Throne/scenarios/04_The_Bay_of_Pearls.cfg

@@ -714,6 +714,7 @@
         [unstore_unit]
             variable=delfador_store
             x,y=31,11
+            find_vacant=yes
         [/unstore_unit]
         # Note: do NOT clear the variable, because Delfador needs to return
         # again in SoE.
@@ -823,6 +824,7 @@
         [unstore_unit]
             variable=delfador_store
             x,y=31,11
+            find_vacant=yes
         [/unstore_unit]
         # Note: do NOT clear the variable, because Delfador needs to return
         # again in SoE.

players_changelog

@@ -3,6 +3,12 @@ changes may be omitted). For a complete list of changes, see the main
 changelog: https://github.com/wesnoth/wesnoth-old/blob/master/changelog
 
 Version 1.11.9+dev:
+ * Campaigns:
+   * Heir to the Throne:
+     * Fixed Delfador clobbering whichever unit happens to be standing on
+       31,11 at the end of The Bay of Pearls, causing it to disappear
+       forever.
+
  * Language and i18n:
    * Updated translations: