[BUG]Error when trying to display XDA Developers categories

[XploreInfinity]

To reproduce:
Go to subscriptions -> Select XDA Developers (under the technology category) -> See the error message "Null check operator used on a null value"

Android version: 11
App version: 0.14.0

Cause: Occurs because the getter categories in lib/extractor/technology/xdadevelopers.dart looks for elements with class name sidenav-link and accesses their href attribute without checking if it exists.

Fix: I tried adding a check that prevents the null value from being passed on to the categories Map, and it works as expected.

I didn't immediately create a PR because the fix is quite small, and there seems to be some problem with tests on my environment. Let me know if you need any help, thanks : )

[ksh-b]

Thanks, should be fixed in next version. This affects androidpolice too I believe.