text: Title: request.post command with  Content-Type set to application/x-www-form-urlencoded expect json from FlareSolverr server
  Body: ### Have you checked our README?
  
  - [X] I have checked the README
  
  ### Have you followed our Troubleshooting?
  
  - [X] I have followed your Troubleshooting
  
  ### Is there already an issue for your problem?
  
  - [X] I have checked older issues, open and closed
  
  ### Have you checked the discussions?
  
  - [X] I have read the Discussions
  
  ### Environment
  
  ```markdown
  - FlareSolverr version: I freshly `git pull`
  - Last working FlareSolverr version: Only used the `git` version
  - Operating system: GNU/Linux
  - Are you using Docker: [yes/no] No
  - FlareSolverr User-Agent (see log traces or / endpoint): User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36
  - Are you using a VPN: [yes/no] No
  - Are you using a Proxy: [yes/no] No
  - Are you using Captcha Solver: [yes/no] No
  - If using captcha solver, which one:
  - URL to test this issue: https://www3.yggtorrent.qa/user/login
  ```
  
  
  ### Description
  
  Hello,
  
  I'm trying to perform a `POST` request using the `request.post` command. The parameters of my request is the following:
  ```
  {'cmd': 'request.post', 'url': 'https://www3.yggtorrent.qa/user/login', 'postData': 'id=someuser&pass=somepassword&ci_csrf_token=', 'session': '1234', 'maxTimeout': 60000, 'returnOnlyCookies': False}
  ```
  Before this request I created a session (so I'm using the same `session_id`) and get the challenge.
  
  But while sending the `request.post` command above, I got the following error from FlareSolverr logs:
  ```
  2024-02-03 21:21:00 ERROR    'NoneType' object is not iterable
  2024-02-03 21:21:00 INFO     127.0.0.1 POST http://127.0.0.1:8191/v1 500 Internal Server Error
  ```
  
  So looking at the souce code I discovered the following in `FlareSolverr.py` (from line 48):
  
  ```
  @app.post('/v1')
  def controller_v1():
      """
      Controller v1
      """
      req = V1RequestBase(request.json)
      res = flaresolverr_service.controller_v1_endpoint(req)
      if res.__error_500__:
          response.status = 500
      return utils.object_to_dict(res)
  ```
  
  The issue is the following line:
  ```
      req = V1RequestBase(request.json)
  ```
  
  So using `request.post` command with `application/x-www-form-urlencoded` does not seem to produce an expected `JSON`. As a result, `request.json` is empty and thus explain the error logs.
  
  
  ### Logged Error Messages
  
  ```text
  2024-02-03 21:21:00 ERROR    'NoneType' object is not iterable
  2024-02-03 21:21:00 INFO     127.0.0.1 POST http://127.0.0.1:8191/v1 500 Internal Server Error
  ```
  
  
  ### Screenshots
  
  _No response_