Summary / Title: [PC/Steam, v1.0.1.58] Battering ram cannot attack standalone walls

Description: In a siege, Battering Rams can only attack city tiles (with walls or fences) if an enemy unit is standing behind the wall (or fence) on that tile. When I try to demolish walls on tiles without an enemy unit, the Battering Ram tries to enter the tile, but it's prohibited due to its class. I tried to use the clickable attack unit action in the tooltip to attack an empty tile, but the same situation happened.

Steps to Reproduce: 

1) Be in a siege with a battering ram unit

2) Move the battering ram next to an empty fortified city tile width wall 

3) Try to attack it, to create a breach.

Reproducibility: 5/5

Expected Behavior: As the unit ability implies "Can only attack walls." it should attack or even destroy the fortification (walls) on empty city tiles as well and not just on tiles with enemy units.

Notes: I only tested it with the base fortification (Fences)

Attachments:

1) Tile without an enemy unit:

Battering_Ram_0.png

Battering_Ram_1.png

2)Tile with an enemy unit: 

Battering_Ram_2.png