Nothing in this chapter shall prevent the restoration or continuance of a nonconforming building or structure which is nonconforming because it fails to comply with any height, area, yard, off-street parking or other like requirements of this chapter, and which is partially destroyed by fire, explosion, act of God, or of any public enemy, or the like; provided, however, that any restoration of any such building or structure shall not enlarge the previously existing nonconformance.