prepare the restored track so the first play is instant

Restore set the window with autoplay = false and never prepared, so the first tap paid
for the connection, the first range request and the startup buffer. Prepare once the
window is set; toggling play then only starts playback.

app/src/main/kotlin/com/subtracks/playback/PlaybackController.kt

@@ -662,6 +662,7 @@ class PlaybackController(
             val position = queueRepository.cursor().coerceIn(0, snapshot.size - 1)
             lastSavedPositionMs = queueRepository.cursorPositionMs().coerceAtLeast(0)
             loadWindow(position, autoplay = false, startPositionMs = lastSavedPositionMs)
+            player?.prepare()
         }
 
     private suspend fun stop() = startLock.withLock { stopLocked() }

app/src/test/kotlin/com/subtracks/playback/PlaybackControllerTest.kt

@@ -144,18 +144,20 @@ class PlaybackControllerTest {
     }
 
     @Test
-    fun togglingPlayOnARestoredQueuePreparesBeforePlaying() {
+    fun aRestoredQueueIsPreparedBeforeTheFirstPlay() {
         seedAlbum(5, sourceId = 1)
         runBlocking { queues.replace(listOf(queues.albumEntry(1, "al1"))) }
 
         controller.connect()
         await { handle.items.isNotEmpty() }
+        await { handle.operations.contains("prepare") }
+
         handle.operations.clear()
 
         controller.togglePlayPause()
         await { handle.operations.contains("play") }
 
-        assertEquals(listOf("prepare", "play"), handle.operations)
+        assertEquals(listOf("play"), handle.operations)
     }
 
     @Test