Abandonment of use of nonconforming building or structure. A building, structure or portion thereof, all or substantially all of which is designed or intended for a use which is not permitted in the district in which it is located, and which is abandoned as of the effective date of this chapter, or thereafter becomes abandoned, shall not thereafter be occupied or used except by a use which conforms to the use regulations of the district in which it is located. However, to constitute an abandonment, it must appear that there is an intent to abandon, and mere cessation or discontinuance of use will not, per se, result in a loss of the right to resume such nonconforming use.