sd: fix incorrect visible center calculation

Don't call PixelToLogic twice. Thanks Ashod for noticing.

Change-Id: Id280dad7e310ceaf8678f900e6e70214848dd925
Reviewed-on: https://gerrit.libreoffice.org/51529Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: pranavk <pranavk@collabora.co.uk>

sd/source/ui/view/sdwindow.cxx

@@ -685,14 +685,8 @@ double Window::GetVisibleHeight()
 
 Point Window::GetVisibleCenter()
 {
-    Size aWinSize = PixelToLogic(GetOutputSizePixel());
-    if ( aWinSize.Height() > maViewSize.Height() )
-        aWinSize.setHeight( maViewSize.Height() );
-    if ( aWinSize.Width() > maViewSize.Width() )
-        aWinSize.setWidth( maViewSize.Width() );
-
     Point aPos;
-    aPos = ::tools::Rectangle(aPos, aWinSize).Center();
+    aPos = ::tools::Rectangle(aPos, GetOutputSizePixel()).Center();
 
     // For LOK
     bool bMapModeWasEnabled(IsMapModeEnabled());