NR S2: change victory condition to prevent unwinnable scenario (fixes #2352)

[ci skip]

Previously, the scenario only ended if you triggered the sighted Hamel event with Tallin.
If you triggered it with any other unit, you wouldn't progress since you can't fire a
sighted event on a unit already visible.

I've changed the condition to move within five hexes of Hamel with Tallin. Still possible
this might result in an unwinnable scenario, but that's much less likely than with what
was there before.

data/campaigns/Northern_Rebirth/scenarios/02_01_Infested_Caves.cfg

@@ -653,7 +653,7 @@
         [objectives]
             side=1
             [objective]
-                description= _ "Speak with Hamel"
+                description= _ "Move Tallin within five hexes of Hamel to speak with him"
                 condition=win
             [/objective]
             {ALTERNATIVE_OBJECTIVE_BONUS ( _ "Clear the caves")}
@@ -674,15 +674,21 @@
         [/objectives]
     [/event]
 
-    # Arriving at the keep, end scenario without bonus.
+    # Moving Tallin withing 5 hexes of Hamel. End scenario without bonus.
+    # TODO: it's possible (but unlikely) that this could result in an unwinnable
+    # scenario if all hexes near Hamel are full. Aagin, though, unlikely. Still,
+    # it might be worth comming up with an even better victory condition.
     [event]
-        name=sighted
+        name=moveto
         [filter]
-            id=Hamel
-        [/filter]
-        [filter_second]
             id=Tallin
-        [/filter_second]
+            [filter_location]
+                [filter]
+                    id=Hamel
+                [/filter]
+                radius=5
+            [/filter_location]
+        [/filter]
 
         [message]
             speaker=Hamel