mysql_stmt_affected_rows()

The problem was that affected_rows for prepared statement wasn't updated
in the client library on the error.  The solution is to always update
affected_rows, which will be equal to -1 on the error.


libmysql/libmysql.c:
  Update status variables even in the case of an error.  Some variables
  have a defined value on the error (like affected_rows is -1), others are
  undefined, so updating them won't harm.
libmysqld/lib_sql.cc:
  Update status variables even in the case of an error.  Some variables
  have a defined value on the error (like affected_rows is -1), others are
  undefined, so updating them won't harm.
tests/mysql_client_test.c:
  Add test for bug#23383: mysql_affected_rows() returns different values
  than mysql_stmt_affected_rows().