fix: Fixes double calls with Target cancel and spell sequences (#1840)

### Summary
- Cleans up target cancellation being called incorrectly.
- An invalid target type (which should never happen), now calls `OnTargetUntargetable` instead of `OnTargetCanceled`
- Removes double calls to `FinishSequence` in Spells.

Projects/UOContent/Spells/Necromancy/EvilOmen.cs

@@ -66,8 +66,6 @@ public class EvilOmenSpell : NecromancerSpell, ISpellTargetingMobile
 
             BuffInfo.AddBuff(m, new BuffInfo(BuffIcon.EvilOmen, 1075647, 1075648, duration, m));
         }
-
-        FinishSequence();
     }
 
     public override void OnCast()
@@ -85,4 +83,4 @@ public class EvilOmenSpell : NecromancerSpell, ISpellTargetingMobile
 
         return false;
     }
-}
+}