Add 'IF EXISTS', otherwise an error would show on MySQL that has no

'gogs' created before.

conf/mysql.sql

@@ -1,2 +1,2 @@
-DROP DATABASE gogs;
-CREATE DATABASE IF NOT EXISTS gogs CHARACTER SET utf8 COLLATE utf8_general_ci;
+DROP DATABASE IF EXISTS gogs;
+CREATE DATABASE IF NOT EXISTS gogs CHARACTER SET utf8 COLLATE utf8_general_ci;