[Applet]Add port check

Summary:
Add port check before port.description check.

Cannot check port.description if port does not exist.

Test Plan:
Before:
If there is a device with ports, and an other one without ports, will fail to display the name a device, or crash?

After:
Name should be displayed correctly in every case.

Reviewers: #plasma, drosca, ngraham

Reviewed By: ngraham

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D27074