FIX: notices and errors in get_connections()

The method get_connections() tries to determine the count of connected entities in a faulty way.
This raises an "undefined property" notice.
Once this is line of code is fixed one gets the following error:

"PHP Fatal error:  Cannot use object of type Entity as array in ..."

This is caused by the following code:
"$this[$connection][$result['entities'][$i]['username']] = $result['entities'][$i];"

Introduced a temporary variable "$tmp_entity" in the for loop for more readability.