Switch server to use new style ManaChange_Struct (#1843)

This will allow us to fix some bugs the current handling has.

Note: the decoder isn't needed since the client always sends it up as a
0 length packet.

zone/spells.cpp

@@ -1001,6 +1001,7 @@ void Mob::StopCasting()
 		mc->stamina = GetEndurance();
 		mc->spell_id = casting_spell_id;
 		mc->keepcasting = 0;
+		mc->slot = -1;
 		c->FastQueuePacket(&outapp);
 	}
 	ZeroCastingVars();
@@ -5218,6 +5219,7 @@ void Mob::SendSpellBarEnable(uint16 spell_id)
 	manachange->spell_id = spell_id;
 	manachange->stamina = CastToClient()->GetEndurance();
 	manachange->keepcasting = 0;
+	manachange->slot = -1;
 	outapp->priority = 6;
 	CastToClient()->QueuePacket(outapp);
 	safe_delete(outapp);