BUG#54744: valgrind reports leak for mysqlbinlog

The server was not cleaning up some 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_end() before the
thread exits.

client/mysqlbinlog.cc

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