Fix memory leak
ASAN trace:
Direct leak of 48 byte(s) in 1 object(s) allocated from:
#0 0x32ff12 in operator new(unsigned long) (/home/kfunk/devel/install/kf5/bin/ruqola+0x32ff12) #1 0x7f50585bdf65 in UsersForRoomModel::parseUsersForRooms(QJsonObject const&, UsersModel*, bool) /home/kfunk/devel/src/kf5/ruqola/src/core/model/usersforroommodel.cpp:186:30 #2 0x7f50586b2032 in RocketChatAccount::parseUsersForRooms(QJsonObject const&, QString const&) /home/kfunk/devel/src/kf5/ruqola/src/core/rocketchataccount.cpp:745:28 ...