Avoid to incluide empty sregex array in rootcheck

[crolopez]

When the remote configuration of Rootcheck is requested, and no sregex ignore has been configured, this array appears empty. The same case happens if not only sregex filters are included.

  <rootcheck>
        <disabled>no</disabled>
        <ignore >path1</ignore>
        <ignore >path2</ignore>
        <ignore >path3</ignore>
  </rootcheck>

curl -u foo:bar -k -X GET "http://127.0.0.1:55000/agents/000/config/syscheck/rootcheck?pretty"
{
   "error": 0,
   "data": {
      "rootcheck": {
         "disabled": "no",
         "scanall": "no",
         "skip_nfs": "no",
         "frequency": 43200,
         "check_dev": "yes",
         "check_files": "no",
         "check_if": "yes",
         "check_pids": "yes",
         "check_ports": "yes",
         "check_sys": "yes",
         "check_trojans": "no",
         "check_unixaudit": "no",
         "ignore": [
            "path1",
            "path2",
            "path3"
         ],
         "ignore_sregex": []
      }
   }
}

This PR solve this invalid behaviour, unifying it with the Syscheck has, and complements #3617.

• Compilation without warnings in every supported platform
  • Linux
  • Windows
  • MAC OS X
• Source installation
• Package installation
• Source upgrade
• Package upgrade
• Memory tests
  • Valgrind report for affected components
  • CPU impact
  • RAM usage impact
• Retrocompatibility with older Wazuh versions