Fix drive.getAudioTitle returning null for no disk

Historically (and according to the docs) getAudioTitle returned "false"
when the drive was empty (or had invalid media), and "null" when the
disk had no item. This was accidentally changed in a later refactor --
this change fixes that behaviour.

projects/common/src/main/java/dan200/computercraft/shared/peripheral/diskdrive/DiskDrivePeripheral.java

@@ -129,7 +129,8 @@ public class DiskDrivePeripheral implements IPeripheral {
     @LuaFunction
     @Nullable
     public final Object getAudioTitle() {
-        return diskDrive.getMedia().getAudioTitle();
+        var stack = diskDrive.getMedia();
+        return stack.media() != null ? stack.getAudioTitle() : false;
     }
 
     /**

projects/common/src/testMod/kotlin/dan200/computercraft/gametest/Disk_Drive_Test.kt

@@ -10,6 +10,7 @@ import dan200.computercraft.gametest.api.*
 import dan200.computercraft.shared.ModRegistry
 import dan200.computercraft.shared.media.items.DiskItem
 import dan200.computercraft.shared.peripheral.diskdrive.DiskDriveBlock
+import dan200.computercraft.shared.peripheral.diskdrive.DiskDrivePeripheral
 import dan200.computercraft.shared.peripheral.diskdrive.DiskDriveState
 import dan200.computercraft.test.core.assertArrayEquals
 import dan200.computercraft.test.core.computer.getApi
@@ -42,6 +43,17 @@ class Disk_Drive_Test {
         }
     }
 
+    /**
+     * [DiskDrivePeripheral] returns `false` when the item is not a disk (or is absent).
+     */
+    @GameTest
+    fun Audio_title_when_empty(helper: GameTestHelper) = helper.sequence {
+        thenOnComputer {
+            callPeripheral("right", "getAudioTitle")
+                .assertArrayEquals(false, message = "Correct audio title")
+        }
+    }
+
     @GameTest
     fun Ejects_disk(helper: GameTestHelper) = helper.sequence {
         val stackAt = BlockPos(2, 2, 2)

projects/common/src/testMod/resources/data/cctest/structures/disk_drive_test.audio_title_when_empty.snbt

@@ -0,0 +1,40 @@
+{
+    DataVersion: 2730,
+    size: [3, 3, 3],
+    data: [
+        {pos: [0, 0, 0], state: "minecraft:polished_andesite"},
+        {pos: [0, 0, 1], state: "minecraft:polished_andesite"},
+        {pos: [0, 0, 2], state: "minecraft:polished_andesite"},
+        {pos: [1, 0, 0], state: "minecraft:polished_andesite"},
+        {pos: [1, 0, 1], state: "minecraft:polished_andesite"},
+        {pos: [1, 0, 2], state: "minecraft:polished_andesite"},
+        {pos: [2, 0, 0], state: "minecraft:polished_andesite"},
+        {pos: [2, 0, 1], state: "minecraft:polished_andesite"},
+        {pos: [2, 0, 2], state: "minecraft:polished_andesite"},
+        {pos: [0, 1, 0], state: "minecraft:air"},
+        {pos: [0, 1, 1], state: "computercraft:disk_drive{facing:north,state:full}", nbt: {id: "computercraft:disk_drive"}},
+        {pos: [0, 1, 2], state: "minecraft:air"},
+        {pos: [1, 1, 0], state: "minecraft:air"},
+        {pos: [1, 1, 1], state: "computercraft:computer_advanced{facing:north,state:blinking}", nbt: {ComputerId: 1, Label: "disk_drive_test.audio_title_when_empty", On: 1b, id: "computercraft:computer_advanced"}},
+        {pos: [1, 1, 2], state: "minecraft:air"},
+        {pos: [2, 1, 0], state: "minecraft:air"},
+        {pos: [2, 1, 1], state: "minecraft:air"},
+        {pos: [2, 1, 2], state: "minecraft:air"},
+        {pos: [0, 2, 0], state: "minecraft:air"},
+        {pos: [0, 2, 1], state: "minecraft:air"},
+        {pos: [0, 2, 2], state: "minecraft:air"},
+        {pos: [1, 2, 0], state: "minecraft:air"},
+        {pos: [1, 2, 1], state: "minecraft:air"},
+        {pos: [1, 2, 2], state: "minecraft:air"},
+        {pos: [2, 2, 0], state: "minecraft:air"},
+        {pos: [2, 2, 1], state: "minecraft:air"},
+        {pos: [2, 2, 2], state: "minecraft:air"}
+    ],
+    entities: [],
+    palette: [
+        "minecraft:polished_andesite",
+        "minecraft:air",
+        "computercraft:disk_drive{facing:north,state:full}",
+        "computercraft:computer_advanced{facing:north,state:blinking}"
+    ]
+}