Fix clamping in BDate::AddMonths():

* use _DaysInMonth() instead of DaysInMonth(), as the latter only works
  for valid dates, which we do not have if the day needs to be clamped
  to the maximum value for the current month


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@42719 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/kits/support/DateTime.cpp

@@ -721,7 +721,7 @@ BDate::AddMonths(int32 months)
 		if (fYear == 1582 && fMonth == 10 && fDay > 4 && fDay < 15)
 			fDay = (months > 0) ? 15 : 4;
 
-		fDay = min_c(fDay, DaysInMonth());
+		fDay = min_c(fDay, _DaysInMonth(fYear, fMonth));
 	}
 }