D28298: Reduce superfluous changedEntriesChanged emissions

[Kai Uwe Broulik]

broulik created this revision.
broulik added reviewers: Frameworks, leinir, ahiemstra.
Herald added a project: Frameworks.
Herald added a subscriber: kde-frameworks-devel.
broulik requested review of this revision.

REVISION SUMMARY
  For some reason I couldn't entirely get behind, `changedEntries` was signalled to change on the QML side on component creation.
  Even when replacing the `Binding` by a direct binding, this wouldn't work. However, while I can't just `alias` it, it turns out, `ghnsDialog` already has a `changedEntries` alias, which we can then just bind to.
  Furthermore, don't signal a change when clearing if it was already empty.
  
  This fixes the wallpaper model in Plasma reloading in-flight, causing thumbnail generation to fail. While this is a genuine bug in the model it only started to be a problem with GHNS needlessly reloading the model.
  
  BUG: 419234

TEST PLAN
  - My thumbnails show up fine again
  - Installing a new thumbnail still reloads the model (`changedEntries` is signalled to change when I install something)

REPOSITORY
  R304 KNewStuff

REVISION DETAIL
  https://phabricator.kde.org/D28298

AFFECTED FILES
  src/qtquick/qml/Button.qml
  src/qtquick/quickengine.cpp

To: broulik, #frameworks, leinir, ahiemstra
Cc: kde-frameworks-devel, LeGast00n, cblack, GB_2, michaelh, ngraham, bruns
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