Handle Esc properly when focus is in searchbox

Summary:
BUG: 408290

If we place the focus in the searchbar, pressing Esc once dismisses the searchbar. However, pressing Esc after this does not dismiss the popup unless one manually intereacts with some other element in the popup. This patch fixes the issue.

Test Plan:
1. Open the Networks popup in the systray.
2. Click the search icon above the channels list.
3. Click in the search area to place focus there.
4. Press Esc. Searchbar disappears.
5. Press Esc again. Check that the popup closes.

Reviewers: #plasma, jgrulich, ngraham

Reviewed By: jgrulich, ngraham

Subscribers: ngraham, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D21620