"0" prefixes are currently not accepted as valid hosts entries

[DandelionSprout]

Prerequisites

• I verified that this is not a filter issue
  • Filter issues MUST be reported at filter issue tracker
• This is not a support issue or a question
  • Support issues and questions are handled at /r/uBlockOrigin
• I performed a cursory search of the issue tracker to avoid opening a duplicate issue
  • Your issue may already be reported.
• I tried to reproduce the issue when...
  • uBlock Origin is the only extension
  • uBlock Origin with default lists/settings
  • using a new, unmodified browser profile
• I am running the latest version of uBlock Origin
• I checked the documentation to understand that the issue I report is not a normal behavior

Description

Currently, 0 example.org does not block the site, whereas ::1 example.org, 127.0.0.1 example.org and 0.0.0.0 example.org does.

This is believed to affect the following lists:

• https://raw.githubusercontent.com/TakoYachty/Gift-Card-Killer/master/Untrusted%20Hosts%20Blocker.txt
• https://raw.githubusercontent.com/arcetera/Minimal-Hosts-Blocker/master/etc/MinimalHostsBlocker/minimalhosts
• https://raw.githubusercontent.com/ReddestDream/reddestdream.github.io/master/Projects/MinimalHostsCB/etc/MinimalHostsBlocker/minimalhosts
• https://raw.githubusercontent.com/ReddestDream/reddestdream.github.io/master/Projects/MinimalHosts/etc/MinimalHostsBlocker/minimalhosts

This is to a certain extent related to #800, but does not seem to me to be a duplicate of it. I'm able to get :: example.org to work in Nano but not in uBO, whereas 0 example.org doesn't work in either of them.

A specific URL where the issue occurs

Depends on the site you'd want to block. For the examples above it's example.org.

Steps to Reproduce

1. Paste 0 example.org in My Filters.
2. Visit example.org.
3. See that no page warnings show up, nor are the (few) on-site elements blocked.

Expected behavior:

A page warning shows up.

Actual behavior:

The site loads normally.

Your environment

• uBlock Origin version: 1.24.2
• Browser Name and version: Vivaldi 2.10.1745.23 64-bit
• Operating System and version: Windows 10 November 2019 Update

[gorhill]

I had to lookup documentation to find out whether this is a valid representation; it is as per Address representations:

When fewer than four numbers are specified in the address in dotted notation, the last value is treated as an integer of as many bytes as are required to fill out the address to four octets.