CGameHandler: fixup healing destination

If it contains hex, not unit, server complains.
Add actual unit there.

server/CGameHandler.cpp

@@ -4898,8 +4898,9 @@ bool CGameHandler::makeBattleAction(BattleAction &ba)
 			{
 				const CSpell * spell = SpellID(healerAbility->subtype).toSpell();
 				spells::BattleCast parameters(gs->curB, healer, spells::Mode::SPELL_LIKE_ATTACK, spell); //We can heal infinitely by first aid tent
+				auto dest = battle::Destination(destStack, target.at(0).hexValue);
 				parameters.setSpellLevel(0);
-				parameters.cast(spellEnv, target);
+				parameters.cast(spellEnv, {dest});
 			}
 			break;
 		}