Race condition issue for curl_global_init and curl_global_cleanup on multi threads

[leventkaragol]

When the curl_global_init and curl_global_cleanup methods are called again on each HttpRequest object, if many HttpRequests are used in parallel in a multi-thread structure, it causes a race condition and causes one thread to cleanup before the other one finishes its work, resulting in undefined behavior. To prevent this, the curl_global_init method should be called once for the first HttpRequest and should not be called again. Similarly, the curl_global_cleanup method must be called once when exiting the application.

However, these calls should not be left to the user. It should be automated with static methods and mutex.