[C++options] Fix previous month and previous quarter at the end of March

.

Because March has more days than February the previous month offset was
getting normalized back to the current month--th 29 February this
year is really 1 March, so normalizing before setting the day caused
begin/end previous month to return the begin/end of the current month.
That probably happened on the 31st of May, July, October, and December
as well, I just hadn't managed to test on those days. Switching the
normalization to after calculating the day of the month broke the
previous quarter calculation because now the month was out of range, so
normalize month & year first.

libgnucash/app-utils/gnc-option-date.cpp

@@ -481,7 +481,11 @@ reldate_set_day_and_time(struct tm& now, RelativeDateType type)
     }
     else if (type == RelativeDateType::END)
     {
-        now.tm_mday = gnc_date_get_last_mday(now.tm_mon, now.tm_year + 1900);
+        /* Ensure that the month is between 0 and 12*/
+        auto year_delta = now.tm_mon / 12 + now.tm_mon < 0 ? -1 : 0;
+        auto month = now.tm_mon - 12 * year_delta;
+        auto year = now.tm_year + year_delta + 1900;
+        now.tm_mday = gnc_date_get_last_mday(month, year);
         gnc_tm_set_day_end(&now);
     }
     // Do nothing for LAST and NEXT.
@@ -559,8 +563,8 @@ gnc_relative_date_to_time64(RelativeDatePeriod period)
             else if (reldate_is_next(period))
                 now.tm_mday += 7;
     }
-    normalize_reldate_tm(now);
     reldate_set_day_and_time(now, checked_reldate(period).m_type);
+    normalize_reldate_tm(now);
     return static_cast<time64>(GncDateTime(now));
 }