fix nextcloud invalid modification time issues

fix_mtime.sh

#!/bin/bash

files=`find . -newermt "0000-12-31 23:59:59" ! -newermt "1970-00-01 23:59:59"`

for filename in $files; do
        touch -a -m "${filename}"
done

# You need to run
# php occ files:scan --all
# to reindex your files to your DB.
# see: https://docs.nextcloud.com/server/latest/admin_manual/configuration_server/occ_command.html#file-operations