when the padding aroun the window changes, update

Summary:
update m_visibleRectBeforeGeometryUpdate when the padding
change signal gets emitted: aurorae updates its shadow
and postentially shadow size asynchronously after repainting.
that would make the first addRepaintDuringGeometryUpdates
when the winow is moved *for the first time* have a wrong
m_visibleRectBeforeGeometryUpdate that doesn't take into
account the shadow, leaving some leftover shadow on screen

BUG:377670

Test Plan:
shadow leftover not reproducible anymore with maui's kwinrc
replaces D4989
tested both on master and together D4990, which should go in as well

Reviewers: #plasma, davidedmundson, graesslin

Reviewed By: #plasma, graesslin

Subscribers: plasma-devel, kwin, #kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D5078

abstract_client.cpp

@@ -85,6 +85,10 @@ AbstractClient::AbstractClient()
         }
     );
 
+    connect(this, &AbstractClient::paddingChanged, this, [this]() {
+        m_visibleRectBeforeGeometryUpdate = visibleRect();
+    });
+
     connect(ApplicationMenu::self(), &ApplicationMenu::applicationMenuEnabledChanged, this, [this] {
         emit hasApplicationMenuChanged(hasApplicationMenu());
     });