Upgrade db, add unique index for download label

app/src/main/java/com/hippo/ehviewer/dao/Database.kt

@@ -109,7 +109,7 @@ class ThumbKeyMigration : AutoMigrationSpec {
 
 @Database(
     entities = [BaseGalleryInfo::class, DownloadEntity::class, DownloadLabel::class, DownloadDirname::class, Filter::class, HistoryInfo::class, LocalFavoriteInfo::class, QuickSearch::class],
-    version = 14,
+    version = 15,
     exportSchema = true,
     autoMigrations = [
         AutoMigration(
@@ -159,6 +159,10 @@ class ThumbKeyMigration : AutoMigrationSpec {
             to = 14,
             spec = GalleryTableMigration::class,
         ),
+        AutoMigration(
+            from = 14,
+            to = 15,
+        ),
     ],
 )
 @TypeConverters(FilterModeConverter::class)

app/src/main/java/com/hippo/ehviewer/dao/DownloadLabel.kt

@@ -2,9 +2,10 @@ package com.hippo.ehviewer.dao
 
 import androidx.room.ColumnInfo
 import androidx.room.Entity
+import androidx.room.Index
 import androidx.room.PrimaryKey
 
-@Entity(tableName = "DOWNLOAD_LABELS")
+@Entity(tableName = "DOWNLOAD_LABELS", indices = [Index("LABEL", unique = true)])
 data class DownloadLabel(
     @ColumnInfo(name = "LABEL")
     var label: String,