Minor bug in string argument validator

In views_handler_argument::validate_argument_basic(), there is this check:

    if (isset($this->definition['numeric']) && !isset($this->options['break_phrase']) && !is_numeric($arg)) {
      return FALSE;
    }

The effect of the first check there is that if $this->definition['numeric'] is defined at all, the field is validated as if it were supposed to be numeric. That is wrong, because if your definition array can specify numeric => TRUE, then you should also be able to specify the default of numeric => FALSE.

Changing the isset() to an empty() is probably sufficient to fix it.