mpNextBackWin is always null now

Change-Id: Idd789433606da3452b9cb0a702abdf549fb1c8d4

vcl/inc/window.h

@@ -105,7 +105,6 @@ struct ImplWinData
 struct ImplOverlapData
 {
     vcl::Region*        mpSaveBackRgn;          //< saved region, which must be invalidated
-    VclPtr<vcl::Window> mpNextBackWin;          //< next window with saved background
 };
 
 struct ImplFrameData

vcl/source/window/clipping.cxx

@@ -810,12 +810,8 @@ void Window::SaveBackground( const Point& rPos, const Size& rSize,
 void Window::ImplInvalidateAllOverlapBackgrounds()
 {
     vcl::Window* pWindow = mpWindowImpl->mpFrameData->mpFirstBackWin;
-    while ( pWindow )
+    if (pWindow)
     {
-        // remember next window here already, as this window could
-        // be removed within the next if clause from the list
-        vcl::Window* pNext = pWindow->mpWindowImpl->mpOverlapData->mpNextBackWin;
-
         if ( ImplIsWindowInFront( pWindow ) )
         {
             Rectangle aRect1( Point( mnOutOffX, mnOutOffY ),
@@ -831,8 +827,6 @@ void Window::ImplInvalidateAllOverlapBackgrounds()
             }
 
         }
-
-        pWindow = pNext;
     }
 }
 

vcl/source/window/window.cxx

@@ -935,7 +935,6 @@ void Window::ImplInit( vcl::Window* pParent, WinBits nStyle, SystemParentData* p
     {
         mpWindowImpl->mpOverlapData                   = new ImplOverlapData;
         mpWindowImpl->mpOverlapData->mpSaveBackRgn    = nullptr;
-        mpWindowImpl->mpOverlapData->mpNextBackWin    = nullptr;
     }
 
     if( pParent && ! mpWindowImpl->mbFrame )