Pre-installed filters cannot be updated

[ameshkov]

Steps to reproduce

1. Install AdGuard Home
2. Run it
3. Go to Filters

Expected result

AdGuard SDN filter has over 30k rules

Actual result

No rules

Errors in the log

2019/10/23 11:00:17 [info] Filter 1 has been updated: 602213 bytes, 31309 rules
2019/10/23 11:00:17 [info] Failed to save the updated filter 1: rename /opt/adguardhome/work/data/filters/1.txt /opt/adguardhome/work/data/filters/1.txt.old: no such file or directory