refactor: SailCollide reuses DockTileIfPort for the soft-landing check

WorldTile already leaves the tile coords in wWX/wGRrow; the open-coded
district shift math was a second copy of what DockTileIfPort does.

Author: splch

src/sail.asm

@@ -679,20 +679,15 @@ SailCollide:
     SR16 h, l, 3
     ld e, l
     ld d, h                        ; de = ty
-    push bc
-    push de
+    ld a, d
+    ld [wGRrowH], a                ; WorldTile stores only ty's low byte
     call WorldTile
-    pop de
-    pop bc
     cp TILE_SAND
     ret c                          ; water: keep sailing
     ; a port district's shore is a dock, not a rock (the same district
-    ; hash that draws the dock planks): stop the ship, spare the hull
-    SR16 b, c, 2
-    ld b, c                        ; dx = tx / 4
-    SR16 d, e, 2
-    ld c, e                        ; dy = ty / 4
-    call HasPortHash
+    ; hash that draws the dock planks): stop the ship, spare the hull.
+    ; WorldTile left the tile coords in wWX/wGRrow for DockTileIfPort.
+    call DockTileIfPort            ; a = TILE_DOCK iff a port district
     ld c, a                        ; survives the revert below (a-only)
     ld a, [wOldPosX]
     ld [wPosX], a
@@ -707,8 +702,8 @@ SailCollide:
     ld [wVelY], a
     call ComputeShipPx
     ld a, c
-    and a
-    ret nz                         ; docking bump: no damage
+    cp TILE_DOCK
+    ret z                          ; docking bump: no damage
     ; hull damage (with cooldown)
     ld a, [wDmgCool]
     and a

src/world.asm

@@ -37,7 +37,7 @@ wFX:            db
 wFY:            db
 wWX::           dw          ; current tile x (generation/detail)
 wGRrow::        db          ; current tile y (low byte; detail hash)
-wGRrowH:        db          ; current tile y, high byte (world rows 256-287)
+wGRrowH::       db          ; current tile y, high byte (world rows 256-287)
 wH00:           db
 wH10:           db
 wH01:           db
@@ -304,7 +304,7 @@ TileAttr:
 ; in: a = TILE_SAND (a beach tile at wWX/wGRrow); out: a = TILE_DOCK if the
 ; tile's 4x4 district is a port district, else TILE_SAND. Pure function of
 ; seed+coords, so streamed and redrawn tiles always agree. clobbers all.
-DockTileIfPort:
+DockTileIfPort::
     ld a, [wWX]
     ld l, a
     ld a, [wWX+1]