Fix more Valgrind uninitialized value errors

1. Base_Thread.cpp: Initialize member variables in constructor
   - curtime, last_move_to_idle_thread_time, epoll_thread, shutdown, mysql_sessions
   were not initialized, causing uninitialized value use in
   ProcessAllMyDS_BeforePoll and ProcessAllMyDS_AfterPoll.

2. MySQL_Logger.cpp: Initialize query_ptr, query_len, and buf in MySQL_Event
   constructor. These fields were used without initialization, causing
   Valgrind errors in JSON serialization and other operations.

lib/Base_Thread.cpp

@@ -22,7 +22,13 @@ template void Base_Thread::register_session(PgSQL_Thread*, PgSQL_Session*, bool)
 template void Base_Thread::run_SetAllSession_ToProcess0<MySQL_Thread, MySQL_Session>();
 template void Base_Thread::run_SetAllSession_ToProcess0<PgSQL_Thread, PgSQL_Session>();
 
-Base_Thread::Base_Thread() {
+Base_Thread::Base_Thread() :
+	curtime(0),
+	last_move_to_idle_thread_time(0),
+	epoll_thread(false),
+	shutdown(0),
+	mysql_sessions(nullptr)
+{
 };
 
 Base_Thread::~Base_Thread() {

lib/MySQL_Logger.cpp

@@ -358,6 +358,8 @@ MySQL_Event::MySQL_Event (log_event_type _et, uint32_t _thread_id, char * _usern
 	start_time=_start_time;
 	end_time=_end_time;
 	query_digest=_query_digest;
+	query_ptr=NULL;
+	query_len=0;
 	client=_client;
 	client_len=_client_len;
 	et=_et;
@@ -377,6 +379,7 @@ MySQL_Event::MySQL_Event (log_event_type _et, uint32_t _thread_id, char * _usern
 	errmsg = nullptr;
 	myerrno = 0;
 	free_on_delete = false; // by default, this is false. This because pointers do not belong to this object
+	memset(buf, 0, sizeof(buf));
 }
 
 MySQL_Event::MySQL_Event(const MySQL_Event &other) {