Manage limit and offset in usersInGroup function
Since user_sql apps don't manage limit and offset in **usersInGroup** function:
`$rows = $this -> helper -> runQuery('getGroupUsers', array('gid' => $gid), false, true);`
The unshareFromGroup function of **Activity** app start a infinity loop :
```
while (!empty($users)) {
$this->addNotificationsForGroupUsers($users, 'unshared_by', $share->getNodeId(), $share->getNodeType(), $share->getTarget(), $share->getId());
$offset += self::USER_BATCH_SIZE;
$users = $group->searchUsers('', self::USER_BATCH_SIZE, $offset);
}
```
to fix that, just add offset and limit params to runQuery :
```
$rows = $this -> helper -> runQuery('getGroupUsers', array('gid' => $gid), false, true, ['limit' => $limit, 'offset' => $offset]);
```
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