LibThread: Uninitialized member variable in Thread, found by Coverity

Author: https://github.com/bgianfo
Commit: 0ca00639a9
Pull-request: https://github.com/SerenityOS/serenity/pull/3184
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/bugaevc

Libraries/LibThread/Thread.h

@@ -45,7 +45,7 @@ public:
 
 private:
     Function<int()> m_action;
-    pthread_t m_tid;
+    pthread_t m_tid { 0 };
     String m_thread_name;
 };