advance past a duplicate song when the playing queued track is deleted

Removing the currently playing track resolved its id against the updated
queue afterwards; if the same song also exists in the context, the lookup
matched that copy and jumped the cursor to it instead of advancing. When the
removed position was the playing one, use the fallback (next in the block /
slot fill) rather than a by-id lookup.

Pre-existing on main, exposed while testing the shuffle rework. Regression
test fails without the fix.

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

@@ -461,6 +461,35 @@ class PlaybackControllerTest {
         }
     }
 
+    @Test
+    fun removingThePlayingQueuedTrackAdvancesPastADuplicateInTheContext() {
+        seedAlbum(4, sourceId = 1)
+        seedSong("y1", "al2")
+
+        controller.playAlbum(1, "al1", 0)
+        await {
+            controller.state.value.item
+                ?.id == "s1"
+        }
+        // "s2" is both queued and in the context; removing the queued copy must advance to the
+        // next queued track, not jump to the identical song in the context.
+        controller.addToQueue(1, QueueKind.Song, "s2")
+        controller.addToQueue(1, QueueKind.Song, "y1")
+        await { runBlocking { controller.upcomingItem()?.id } == "s2" }
+        controller.playAt(1)
+        await {
+            controller.state.value.item
+                ?.id == "s2"
+        }
+
+        runBlocking { controller.removeAt(1) }
+
+        await {
+            controller.state.value.item
+                ?.id == "y1"
+        }
+    }
+
     @Test
     fun playNextFromInsideTheBlockGoesAfterTheCurrentTrack() {
         seedAlbum(3, sourceId = 1)