More CppunitTest_sw_uiwriter fixes

1) Guard against nDPI == 0 in ImplLogicToPixel(), it's the caller's
responsibility to ensure that the DPI value is in the expected range.

2) pOut in sdr::overlay::impCheckPossibleOverlayType() is seen as 0.

Change-Id: Iab5ff10aa7953993161dcad2d49d99d80c588e01

sc/source/core/data/patattr.cxx

@@ -392,7 +392,7 @@ void ScPatternAttr::GetFont(
         Size aSize( 0, (long) nFontHeight );
         MapMode aDestMode = pOutDev->GetMapMode();
         MapMode aSrcMode( MAP_TWIP, Point(), aFraction, aFraction );
-        if (aDestMode.GetMapUnit() == MAP_PIXEL)
+        if (aDestMode.GetMapUnit() == MAP_PIXEL && pOutDev->GetDPIX() > 0)
             aEffSize = pOutDev->LogicToPixel( aSize, aSrcMode );
         else
         {

svx/source/sdr/overlay/overlayselection.cxx

@@ -72,9 +72,8 @@ namespace sdr
                     // not possible when switched off by user
                     return OVERLAY_INVERT;
                 }
-                else
+                else if (const OutputDevice* pOut = Application::GetDefaultDevice())
                 {
-                    const OutputDevice *pOut = Application::GetDefaultDevice();
 
                     if(pOut->GetSettings().GetStyleSettings().GetHighContrastMode())
                     {