[fix] lock request pool generator

import requests

from itertools import cycle

from threading import RLock

from searx import settings

        super(SessionSinglePool, self).__init__()

        # reuse the same adapters

        with RLock():

            self.adapters.clear()

            self.mount('https://', next(https_adapters))

            self.mount('http://', next(http_adapters))

def request(method, url, **kwargs):

    """same as requests/requests/api.py request(...) except it use SessionSinglePool and force proxies"""

    global settings

    session = SessionSinglePool()

    kwargs['proxies'] = settings['outgoing'].get('proxies', None)

    response = session.request(method=method, url=url, **kwargs)