Add minor safety to DROP INDEX/TABLE statements in migrations

migrations/11_add_reserved_ids_table_down.sql

-DROP INDEX reserved_media_index;
-DROP TABLE reserved_media;
+DROP INDEX IF EXISTS reserved_media_index;
+DROP TABLE IF EXISTS reserved_media;

migrations/13_add_export_tables_down.sql

-DROP INDEX export_parts_index;
-DROP TABLE export_parts;
-DROP TABLE exports;
+DROP INDEX IF EXISTS export_parts_index;
+DROP TABLE IF EXISTS export_parts;
+DROP TABLE IF EXISTS exports;

migrations/16_add_media_attributes_table_down.sql

-DROP INDEX idx_media_attributes_purpose;
-DROP INDEX idx_media_attributes;
-DROP TABLE media_attributes;
+DROP INDEX IF EXISTS idx_media_attributes_purpose;
+DROP INDEX IF EXISTS idx_media_attributes;
+DROP TABLE IF EXISTS media_attributes;

migrations/1_create_tables_down.sql

-DROP INDEX media_index;
-DROP INDEX thumbnails_index;
-DROP INDEX url_previews_index;
-DROP TABLE url_previews;
-DROP TABLE thumbnails;
-DROP TABLE media;
+DROP INDEX IF EXISTS media_index;
+DROP INDEX IF EXISTS thumbnails_index;
+DROP INDEX IF EXISTS url_previews_index;
+DROP TABLE IF EXISTS url_previews;
+DROP TABLE IF EXISTS thumbnails;
+DROP TABLE IF EXISTS media;

migrations/20_create_id_hold_table_down.sql

-DROP INDEX idx_media_id_hold;
-DROP TABLE media_id_hold;
\ No newline at end of file
+DROP INDEX IF EXISTS idx_media_id_hold;
+DROP TABLE IF EXISTS media_id_hold;
\ No newline at end of file

migrations/2_add_animated_col_down.sql

-DROP INDEX thumbnails_index;
+DROP INDEX IF EXISTS thumbnails_index;
 CREATE UNIQUE INDEX IF NOT EXISTS thumbnails_index ON thumbnails (media_id, origin, width, height, method);
 ALTER TABLE thumbnails DROP COLUMN animated;

migrations/2_add_animated_col_up.sql

 ALTER TABLE thumbnails ADD COLUMN animated BOOL NOT NULL DEFAULT FALSE;
-DROP INDEX thumbnails_index;
+DROP INDEX IF EXISTS thumbnails_index;
 CREATE UNIQUE INDEX IF NOT EXISTS thumbnails_index ON thumbnails (media_id, origin, width, height, method, animated);

migrations/6_track_last_accessed_times_down.sql

-DROP INDEX last_access_index;
-DROP TABLE last_access;
+DROP INDEX IF EXISTS last_access_index;
+DROP TABLE IF EXISTS last_access;

migrations/7_add_datastore_down.sql

 ALTER TABLE media DROP COLUMN datastore_id;
 ALTER TABLE thumbnails DROP COLUMN datastore_id;
-DROP INDEX datastores_index;
-DROP TABLE datastores;
+DROP INDEX IF EXISTS datastores_index;
+DROP TABLE IF EXISTS datastores;