sc tiled rendering: We keep increasing the precision here...

... so let's finally do it right, and count in double precision directly.

Change-Id: Ic49cc42d9e61a1b9fa9853bfe93d2681a6be88b2

sc/source/core/data/global.cxx

@@ -519,9 +519,9 @@ void ScGlobal::Init()
 void ScGlobal::InitPPT()
 {
     OutputDevice* pDev = Application::GetDefaultDevice();
-    Point aPix1000 = pDev->LogicToPixel( Point(100000,100000), MapUnit::MapTwip );
-    nScreenPPTX = aPix1000.X() / 100000.0;
-    nScreenPPTY = aPix1000.Y() / 100000.0;
+
+    nScreenPPTX = double(pDev->GetDPIX()) / double(TWIPS_PER_INCH);
+    nScreenPPTY = double(pDev->GetDPIY()) / double(TWIPS_PER_INCH);
 }
 
 const OUString& ScGlobal::GetClipDocName()