UnboundLocalError: local variable 'err' referenced before assignment

### Step 1: Please describe your environment

* ZeroNet version: 0.7.2 r4555
* Operating system: Devuan Chimaera 4.0
* Web browser: Firefox ESC
* Tor status: enabled/available
* Opened port: yes
* Special configuration: `$ cat zeronet.conf
[global]
open_browser = False
threads_crypt = 3
threads_fs_write = 2
threads_fs_read = 4
language = en
fileserver_ip_type = ipv4`

### Step 2: Describe the problem: While running `siteVerify` on a large site, I get the said error message:
````
$ python3 ./core/zeronet.py siteVerify 1TaLkFrMwvbNsooF4ioKAY9EuxTBTjipT
- Starting ZeroNet...
PluginManager Plugin Bigfile load error: ModuleNotFoundError: No module named 'merkletools' in PluginManager.py line 138 > Bigfile/__init__.py line 1 > BigfilePlugin.py line 20
PluginManager Plugin CryptMessage load error: ModuleNotFoundError: No module named 'base58' in PluginManager.py line 138 > CryptMessage/__init__.py line 1 > CryptMessagePlugin.py line 7 > CryptBitcoin.py line 14 > lib/sslcrypto/__init__.py line 4 > lib/sslcrypto/openssl/__init__.py line 1 > lib/sslcrypto/openssl/aes.py line 4 > lib/sslcrypto/fallback/__init__.py line 2 > lib/sslcrypto/fallback/ecc.py line 4 > lib/sslcrypto/_ecc.py line 4
- Version: 0.7.2 r4555, Python 3.9.2 (default, Feb 28 2021, 17:03:44)
[GCC 10.2.1 20210110], Gevent: 22.10.2
SiteManager Loading sites... (cleanup: True, startup: False)
SiteManager Added 44 sites in 0.098s
Db#2:ContentDb Loaded 257792 optional files: 1191006.56MB, downloaded: 290.05MB in 0.464s
- Verifing site: 1TaLkFrMwvbNsooF4ioKAY9EuxTBTjipT...
- Verifing content.json signature...
- Unhandled exception: local variable 'err' referenced before assignment
Traceback (most recent call last):
File "/home/quix0r/ZeroNet-linux-dist-linux64/./core/zeronet.py", line 17, in main
main.start()
File "/home/quix0r/ZeroNet-linux-dist-linux64/core/src/main.py", line 602, in start
actions.call(config.action, action_kwargs)
File "/home/quix0r/ZeroNet-linux-dist-linux64/core/src/main.py", line 133, in call
back = func(**kwargs)
File "/home/quix0r/ZeroNet-linux-dist-linux64/core/src/main.py", line 263, in siteVerify
logging.error("[ERROR] %s: invalid file: %s!" % (content_inner_path, err))
UnboundLocalError: local variable 'err' referenced before assignment

````
PS: I had to install missing `gevent` through `pip` before. The version from my distribution is rather old (20.9.0-2 versus 22.10.2) or otherwise a simple `$ python3 ./core/zeronet.py --version` doesn't work.

#### Steps to reproduce:

1. Just execute the above command, or try an other site white ZeroNet is running.

#### Observed Results:

* I got the above error message.

#### Expected Results:

* The command runs through without any error messages.