Any nonconforming structure existing at the time of the passage of this chapter may be restored or repaired in the event of partial destruction thereof, provided that said structure or use thereof is not abandoned. Nothing in this chapter shall prevent any such existing nonconforming structure from being restored to a safe condition or from being repaired, reconstructed or structurally altered, provided that such restoration, repair, reconstruction or alteration would comply with all other municipal regulations and ordinances; and provided, further, that no restoration, repair, reconstruction or alteration shall in any way enlarge or extend any nonconforming structure or nonconforming use.