loxberry_system.php: Fixed pluginversion() returns NULL
loxberry_system.php: Fixed pluginversion() returns NULL

- Fixed checked wrong plugindb property
- Now checks PLUGINDB_NAME and PLUGINDB_FOLDER

mschlenstedt/Loxberry,mschlenstedt/Loxberry,mschlenstedt/Loxberry,mschlenstedt/Loxberry,mschlenstedt/Loxberry,mschlenstedt/Loxberry