verify sign error: ValueError: Extra data: line 3140 column 2 - line 3140 column 103

### Step 1: Please describe your environment

* ZeroNet version: 0.6.1 r2324
* Operating system: Debian buster
* Web browser: 52.6.0
* Tor status: always
* Opened port: yes
* Special configuration: in /etc/tor
```
ControlPort 9051
CookieAuthentication 1
```

From https://zeronet.readthedocs.io/en/latest/faq/#how-to-make-zeronet-work-with-tor-under-linux

### Step 2: Describe the problem:

Got the following output while running zeronet

[11:52:49] Site:1PLAYg..Xvfp content.json: verify sign error: ValueError: Extra data: line 3140 column 2 - line 3140 column 103 (char 108699 - 108800) in ContentManager.py line 821 > __init__.py line 291 > __init__.py line 339 > decoder.py line 367

#### Steps to reproduce:

#### Observed Results:

The same as above.

#### Expected Results:

The error should not be there.

If such an error does happen, at least give some hint as to where I should look next to resolve it.

Start with the reported traceback at ContentManager.py line 821 and follow it through decoder.py line 367 while examining the affected content.json around line 3140. Reproduce the verification error in the reported ZeroNet 0.6.1 environment, then confirm that the failure is either resolved or provides a useful next-step diagnostic.

索引モデルが issue の本文から書いたものです。