Fix stale Lucene reader after ratings index rebuild

The reader and searcher were lazily initialized once, so after
rebuild() created a new index, searches still used the old reader
pointing to outdated document IDs. When those IDs were used to
index into the new players array, wrong entries were returned.

Now reader/searcher are refreshed after each build().

view-webapp/src/main/kotlin/org/jeudego/pairgoth/ratings/PlayerIndex.kt

@@ -39,8 +39,8 @@ class PlayerIndex {
         val stopChars = Regex("[_-]")
     }
     private final val directory: Directory = ByteBuffersDirectory(NoLockFactory.INSTANCE)
-    private val reader by lazy { DirectoryReader.open(directory) }
-    private val searcher by lazy { IndexSearcher(reader) }
+    private lateinit var reader: DirectoryReader
+    private lateinit var searcher: IndexSearcher
 
     // helper functions
     fun Json.Object.field(key: String) = getString(key) ?: throw Error("missing $key")
@@ -68,6 +68,9 @@ class PlayerIndex {
                 ++count
             }
         }
+        // Refresh reader and searcher to see the new index
+        reader = DirectoryReader.open(directory)
+        searcher = IndexSearcher(reader)
         logger.info("indexed $count players")
     }