BUG#54744: valgrind reports leak for mysqlbinlog

The server was not cleaning up dbug allocated memory before
exiting. This is not a real problem, as this memory would be
deallocated anyway. Nonetheless, we improve the mysqlbinlog exit
procedure, wrt to memory book-keeping, when no parameter is
given.

To fix this, we deploy a call to my_thread_end() before the
thread exits, which will also free pending dbug related allocated
blocks.

client/mysqlbinlog.cc

@@ -2032,6 +2032,7 @@ int main(int argc, char** argv)
   {
     usage();
     free_defaults(defaults_argv);
+    my_thread_end();
     exit(1);
   }