fdo#70861 SwToSfxPageDescAttr: fix call to SvxExtParagraphTabPage

Regression from c2ccd20c (fdo#44689: fix
for specific case of page restart-value 0, 2013-08-29), the problem was
that commit refactored starting page number handling, so that '0' is now
also a valid value, and no longer means "no restart". However cui isn't
updated yet, so always pass a 0 to it, like we used to do so before,
that's better than a crash.

Change-Id: I2adab43499bcdd5234da3f26559b0b384e533c2e

sw/source/ui/utlui/uitool.cxx

@@ -642,9 +642,10 @@ void SwToSfxPageDescAttr( SfxItemSet& rCoreSet )
         bPut = false;
     }
 
-    if (oNumOffset)
+    // TODO for now always pass a page number to cui, it can't make a
+    // difference between 0 and no page number at the moment.
     {
-        SfxUInt16Item aPageNum( SID_ATTR_PARA_PAGENUM, oNumOffset.get() );
+        SfxUInt16Item aPageNum( SID_ATTR_PARA_PAGENUM, oNumOffset ? oNumOffset.get() : 0 );
         rCoreSet.Put( aPageNum );
     }