QDockAreaLayout: use QSignalBlocker

This change changes the point where signals are unblocked again in
QDockAreaLayoutInfo::updateTabBar() to include the final tabBar->count()
call. This should not be a problem, as count() is a const function and
thus shouldn't emit any signals.

Change-Id: I6f3dc5696a9c31db51fbe4cdee4b9d83ddeaf61f
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

src/widgets/widgets/qdockarealayout.cpp

@@ -2096,7 +2096,7 @@ bool QDockAreaLayoutInfo::updateTabBar() const
         that->tabBar->setDrawBase(true);
     }
 
-    bool blocked = tabBar->blockSignals(true);
+    const QSignalBlocker blocker(tabBar);
     bool gap = false;
 
     int tab_idx = 0;
@@ -2147,8 +2147,6 @@ bool QDockAreaLayoutInfo::updateTabBar() const
         tabBar->removeTab(tab_idx);
     }
 
-    tabBar->blockSignals(blocked);
-
     //returns if the tabbar is visible or not
     return ( (gap ? 1 : 0) + tabBar->count()) > 1;
 }