[PanelView] Emit availableScreenRegionChanged in resizeEvent, not when setting a new length

The panel length might not actually change depending on minimum and maximum size constraints
and this is the wrong place to do this in the first place.

Differential Revision: https://phabricator.kde.org/D4590

shell/panelview.cpp

@@ -228,7 +228,6 @@ void PanelView::setLength(int value)
     m_contentLength = value;
 
     resizePanel();
-    emit m_corona->availableScreenRegionChanged();
 }
 
 int PanelView::maximumLength() const
@@ -708,6 +707,8 @@ void PanelView::resizeEvent(QResizeEvent *ev)
         m_shellSurface->setPosition(pos);
     }
     m_strutsTimer.start(STRUTSTIMERDELAY);
+    emit m_corona->availableScreenRegionChanged();
+
     PlasmaQuick::ContainmentView::resizeEvent(ev);
 }