Bug#43706: libmysqld segfaults when re-intialised

Bug#44091: libmysqld gets stuck waiting on mutex on initialization

The problem was that libmysqld wasn't enforcing a certain
initialization and deinitialization order for the mysys
library. Another problem was that the global object used
for management of log event handlers (aka LOGGER) wasn't
being prepared for a possible reutilization.

What leads to the hang/crash reported is that a failure
to load the language file triggers a double call of the
cleanup functions, causing an already destroyed mutex to
be used.

The solution is enforce a order on the initialization and
deinitialization of the mysys library within the libmysqld
library and to ensure that the global LOGGER object reset
it's internal state during cleanup.

mysys/my_init.c

@@ -136,6 +136,10 @@ void my_end(int infoflag)
   */
   FILE *info_file= DBUG_FILE;
   my_bool print_info= (info_file != stderr);
+
+  if (!my_init_done)
+    return;
+
   /*
     We do not use DBUG_ENTER here, as after cleanup DBUG is no longer
     operational, so we cannot use DBUG_RETURN.

sql/log.cc

@@ -845,6 +845,7 @@ void LOGGER::cleanup_base()
   {
     table_log_handler->cleanup();
     delete table_log_handler;
+    table_log_handler= NULL;
   }
   if (file_log_handler)
     file_log_handler->cleanup();
@@ -855,7 +856,11 @@ void LOGGER::cleanup_end()
 {
   DBUG_ASSERT(inited == 1);
   if (file_log_handler)
+  {
     delete file_log_handler;
+    file_log_handler=NULL;
+  }
+  inited= 0;
 }