util/mesa-db: Recreate files if header load or index update fails

The previous behaviour had these issues:

1. It meant that this part of the cache couldn't be used
   this time.
2. It left the corrupted index/cache files unchanged, so the same failure
   might happen again next time.

Recreating the index & cache files for this part means it can be used,
it just loses any previously cached contents.

Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Acked-by: Timothy Arceri <tarceri@itsqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30988>

src/util/mesa_cache_db.c

@@ -335,10 +335,6 @@ mesa_db_load(struct mesa_cache_db *db, bool reload)
        !mesa_db_load_header(&db->index) ||
        db->cache.uuid != db->index.uuid) {
 
-      /* This is unexpected to happen on reload, bail out */
-      if (reload)
-         goto fail;
-
       if (!mesa_db_recreate_files(db))
          goto fail;
    } else {
@@ -350,8 +346,16 @@ mesa_db_load(struct mesa_cache_db *db, bool reload)
    if (reload)
       mesa_db_hash_table_reset(db);
 
-   if (!mesa_db_update_index(db))
-      goto fail;
+   /* The update failed so we assume the files are corrupt and
+    * recreate them.
+    */
+   if (!mesa_db_update_index(db)) {
+      mesa_db_recreate_files(db);
+      db->index.offset = ftell(db->index.file);
+
+      if (!mesa_db_update_index(db))
+         goto fail;
+   }
 
    if (!reload)
       mesa_db_unlock(db);