Activity report SQL syntax error

After installing 4.7.23, the "Scheduled Activities" dashlet causes a "Network Error : unable to reach the server" popup, and the dashlet does not populate.

Looks like there is an error in the SQL statement around line 870 of Report/Form/Activity.php.

When "$this->_aclWhere" is NULL, the WHERE statement resolves as WHERE (1) AND GROUP BY, which throws a syntax error.

I fixed it by adding an IF clause to ensure that the AND isn't included if "$this->_aclWhere" is empty.