API: Fix setnotificationtimestamp with no pages given

When newerthanrevid or torevid is used and no pages are given, do not
throw a fatal PHP error.

When no pages are given in other modes, do not return a database error.

Bug: 48071
Change-Id: I5abcdf0fa20486f1198d1cc111461b3088a311df
Merge "API: Fix setnotificationtimestamp with no pages given"