Add validation to error out invalid input

[SophieFriederike]

Describe the bug

"Found 0 subdomains for https://votemanager.de/ in 11 seconds 335 milliseconds"
There has to be at least one subdomain, but I am not sure why it didn´t find it...
(https://wahlen.votemanager.de/)


**Subfinder version**
Include the version of subfinder you are using, `subfinder -version`
[INF] Current subfinder version v2.6.7 (latest)


**Complete command you used to reproduce this**
┌──(root㉿kali)-[~]
└─# subfinder -d https://votemanager.de/ -all

               __    _____           __         
   _______  __/ /_  / __(_)___  ____/ /__  _____
  / ___/ / / / __ \/ /_/ / __ \/ __  / _ \/ ___/
 (__  ) /_/ / /_/ / __/ / / / / /_/ /  __/ /    
/____/\__,_/_.___/_/ /_/_/ /_/\__,_/\___/_/

                projectdiscovery.io

[INF] Current subfinder version v2.6.7 (latest)
[INF] Loading provider config from /root/.config/subfinder/provider-config.yaml
[INF] Enumerating subdomains for https://votemanager.de/
[INF] Found 0 subdomains for https://votemanager.de/ in 11 seconds 335 milliseconds

Screenshots
Add screenshots of the error for a better context.

[ola456]

The tool expects just the domain (not url), so something like subfinder -d votemanager.de should work

[SophieFriederike]

The tool expects just the domain (not url), so something like subfinder -d votemanager.de should work

Thx