Fix "Add Network Folder" tooltip icon does not show on Breeze, shows correctly on...

Fix "Add Network Folder" tooltip icon does not show on Breeze, shows correctly on Breeze Dark

Summary:
Fix "Add Network Folder" tooltip icon does not show on Breeze, shows correctly
on Breeze Dark. The fix is taken from D19596.

Test Plan:
Open Dolphin with the Breeze theme
Hover the mouse over the "Add Network Folder"
The icon is black on black

BUG: 404858

Reviewers: #dolphin, elvisangelaccio, ngraham

Reviewed By: #dolphin, elvisangelaccio, ngraham

Subscribers: broulik, kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D19738