lib: fix batch-size after db creation

Ensure we use the user-specified batch-size immediately after db creation.

lib/mu-xapian-db.hh

@@ -222,6 +222,14 @@ public:
 			mu_debug("closing db");
 	}
 
+	/**
+	 * Reinitialize from inner-config. Needed after CreateOverwrite.
+	 *
+	 * This is bit of a hack, needed since we cannot setup the config
+	 * before we have a database.
+	 */
+	void reinit();
+
 	/**
 	 * Is the database read-only?
 	 *
@@ -545,7 +553,7 @@ private:
 	std::string path_;
 	DbType	db_;
 	size_t	tx_level_{};
-	const size_t batch_size_;
+	size_t batch_size_;
 	size_t changes_{};
 };