MariaBackup: gcc7 - snprintf output overflow warning

extra/mariabackup/xtrabackup.cc: In function ‘ulint xb_process_datadir(const char*, const char*, handle_datadir_entry_func_t)’:
extra/mariabackup/xtrabackup.cc:4534:1: warning: ‘snprintf’ output may be truncated before the last format character [-Wformat-truncation=]
 xb_process_datadir(
 ^~~~~~~~~~~~~~~~~~
mariabackup/xtrabackup.cc:4607:11: note: ‘snprintf’ output 2 or more bytes (assuming 4001) into a destination of size 4000
   snprintf(dbpath, sizeof(dbpath), "%s/%s", path, dbinfo.name);
   ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

extra/mariabackup/xtrabackup.cc

@@ -4538,7 +4538,7 @@ xb_process_datadir(
 	handle_datadir_entry_func_t	func)	/*!<in: callback */
 {
 	ulint		ret;
-	char		dbpath[OS_FILE_MAX_PATH];
+	char		dbpath[OS_FILE_MAX_PATH+1];
 	os_file_dir_t	dir;
 	os_file_dir_t	dbdir;
 	os_file_stat_t	dbinfo;
@@ -4604,7 +4604,7 @@ xb_process_datadir(
 		        goto next_datadir_item;
 		}
 
-		snprintf(dbpath, sizeof(dbpath), "%s/%s", path, dbinfo.name);
+		snprintf(dbpath, sizeof(dbpath)-1, "%s/%s", path, dbinfo.name);
 
 		os_normalize_path(dbpath);