sort: fix sort bug with same-year album songs

Fix a problem where given two albums with the same year, like this:

Album 1 [2018]
- Song 1
- Song 2

Album 2 [2018]
- Song 3
- Song 4

getSortedArtistSongs would incorrectly drop songs that came from
any albums that came after Album 1, resulting in this:

Song 1 [Album 1]
Song 2 [Album 1]

This was caused by a quirk in toSortedMap that would drop any
map entries that corresponded to a previous sorted entry. We now
get and sort the entries directly instead, which fixes the issue.

app/src/main/java/org/oxycblt/auxio/recycler/SortMode.kt

@@ -144,8 +144,8 @@ enum class SortMode(@DrawableRes val iconRes: Int) {
             NUMERIC_UP -> {
                 val list = mutableListOf<Song>()
 
-                songs.groupBy { it.album }.toSortedMap(compareBy { it.year }).values.forEach { items ->
-                    list.addAll(items.sortedWith(compareBy { it.track }))
+                songs.groupBy { it.album }.entries.sortedBy { it.key.year }.forEach { entry ->
+                    list.addAll(entry.value.sortedWith(compareBy { it.track }))
                 }
 
                 list
@@ -154,8 +154,8 @@ enum class SortMode(@DrawableRes val iconRes: Int) {
             NUMERIC_DOWN -> {
                 val list = mutableListOf<Song>()
 
-                songs.groupBy { it.album }.toSortedMap(compareByDescending { it.year }).values.forEach { items ->
-                    list.addAll(items.sortedWith(compareBy { it.track }))
+                songs.groupBy { it.album }.entries.sortedWith(compareByDescending { it.key.year }).forEach { entry ->
+                    list.addAll(entry.value.sortedWith(compareBy { it.track }))
                 }
 
                 list