db/Configured: convert path to UTF-8 before injecting into configuration

src/db/Configured.cxx

@@ -60,9 +60,12 @@ CreateConfiguredDatabase(EventLoop &loop, DatabaseListener &listener,
 			return nullptr;
 
 		const auto db_file = AllocatedPath::Build(cache_dir, "mpd.db");
+		const auto db_file_utf8 = db_file.ToUTF8();
+		if (db_file_utf8.empty())
+			return nullptr;
 
 		allocated = new ConfigBlock();
-		allocated->AddBlockParam("path", db_file.c_str(), -1);
+		allocated->AddBlockParam("path", db_file_utf8.c_str(), -1);
 		param = allocated;
 	}