Stop boulders being pushed through walls (#754)

checkBoulderPush had an isWarpTileCell escape hatch that let a boulder
be pushed onto any door/warp tile, walkable or not. In pokered,
CheckForCollisionWhenPushingBoulder walks the same wTilesetCollisionPtr
list as player movement (CheckTilePassable) -- there is no hole/warp
exception, so a boulder can never land on a cell the player cannot walk
onto.

The known push targets (CAVERN  holes, Victory Road switches) are
walkable tiles in their tileset's coll list already, so removing the
escape hatch only stops pushing boulders into walls.

Fixes #754

src/world/OverworldController.lua

@@ -1216,12 +1216,16 @@ function OverworldState:checkBoulderPush(dir)
   end
   local bx, by = Collision.target(fx, fy, dir)
   if not self.map:inBounds(bx, by) then self.boulderTried = nil return false end
+  -- CheckForCollisionWhenPushingBoulder uses the same walkable check as
+  -- player movement (CheckTilePassable walks the same wTilesetCollisionPtr
+  -- list) -- there is no hole/warp escape hatch in the original, so a
+  -- boulder can never be pushed onto a cell the player cannot walk onto.
+  -- The known push targets (CAVERN $22 holes, Victory Road switches) are
+  -- walkable tiles in their tileset's coll list already, so removing the
+  -- port's isWarpTileCell exception only stops wall pushes (#754).
   if not self.map:isWalkableCell(bx, by) then
-    -- boulders may be pushed into holes/switch spots that aren't walkable
-    if not self.map:isWarpTileCell(bx, by) then
-      self.boulderTried = nil
-      return false
-    end
+    self.boulderTried = nil
+    return false
   end
   if Collision.occupied(self.entities, bx, by, npc) then
     self.boulderTried = nil