Calculate null-date days to assert only once

Massively called it is really unnecessary to do that each and
every time. The debug build is slow enough..

Change-Id: I06525e4ca1fa23a1d49dd735370eb157157800e7
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/143127
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Jenkins

comphelper/source/misc/date.cxx

@@ -100,7 +100,10 @@ sal_Int32 convertDateToDaysNormalizing(sal_uInt16 nDay, sal_uInt16 nMonth, sal_I
     // Speed-up the common null-date 1899-12-30.
     if (nYear == 1899 && nDay == 30 && nMonth == 12)
     {
-        assert(convertDateToDays(nDay, nMonth, nYear) == 693594);
+#ifndef NDEBUG
+        static sal_Int32 nDays = convertDateToDays(nDay, nMonth, nYear);
+        assert(nDays == 693594);
+#endif
         return 693594;
     }
     normalize(nDay, nMonth, nYear);

tools/source/datetime/tdate.cxx

@@ -72,7 +72,10 @@ sal_Int32 Date::GetAsNormalizedDays() const
     // This is a very common datum we often calculate from.
     if (mnDate == 18991230) // 1899-12-30
     {
-        assert(DateToDays( GetDay(), GetMonth(), GetYear() ) == 693594);
+#ifndef NDEBUG
+        static sal_Int32 nDays = DateToDays( GetDay(), GetMonth(), GetYear());
+        assert(nDays == 693594);
+#endif
         return 693594;
     }
     // Not calling comphelper::date::convertDateToDaysNormalizing() here just