Cases where json_object_get() returns INVALID_HANDLE

[Selena-Gomez]

In the sourcepawn native json_object_get_float() (and possibly others), where json_object_get() is used, the error case of json_object_get() is not covered.
For the store plugin, this leads to errors in console if an item does not have a specific attribute.
Tough it's possible to overcome this by checking if json_object_get(Handle, attribute string) returns INVALID_HANDLE, before calling json_object_get_float() and the like.