fix: door spawn required wall be exist on the cells that don't matter

src/net/torvald/terrarum/Terrarum.kt

@@ -1013,3 +1013,9 @@ fun distBetween(a: ActorWithBody, bpos: Vector2): Double {
 }
 const val hashStrMap = "YBNDRFG8EJKMCPQXOTLVWIS2A345H769"
 fun getHashStr(length: Int = 5) = (0 until length).map { hashStrMap[Math.random().times(32).toInt()] }.joinToString("")
+
+fun <S, T> List<S>.cartesianProduct(other: List<T>) = this.flatMap { thisIt ->
+    other.map { otherIt ->
+        thisIt to otherIt
+    }
+}