Incorrect Dec. 31 sowing prevents sowing in first year

### Brief summary of bug

In older versions of CLM, the use of `get_curr_calday()` instead of `get_prev_calday()` would sometimes cause crops to be sown in the last timestep of Dec. 31 when their sowing window didn't actually start until Jan. 1. Newer versions are supposed to handle this by detecting such incorrect sowings and harvesting immediately, but they don't.

### General bug information

**CTSM version you are using:** `ctsm5.1.dev142`

**Does this bug cause significantly incorrect results in the model's science?** Only in the first year after resuming from an old restart.

**Configurations affected:** All crop compsets.

### Details of bug

This is the code that tells CLM to harvest when an "incorrectly sown on Dec. 31" patch is detected (`idop` = day of planting, `jday` = day of year today, `sowing_count` = number of sowings this calendar year, `sdates_thisyr_patch` = list of sowing dates this calendar year):
https://github.com/ESCOMP/CTSM/blob/2e2434d10e35404be5284022270f474d50d2db26/src/biogeochem/CNPhenologyMod.F90#L2153-L2157

(Note that when a crop was incorrectly sown in the last timestep of Dec. 31, its `idop` would be set misleadingly to 1.)

This harvest never happens because, earlier in `CropPhenology()`, such patches get their `sowing_count` set to 1:
https://github.com/ESCOMP/CTSM/blob/2e2434d10e35404be5284022270f474d50d2db26/src/biogeochem/CNPhenologyMod.F90#L1928-L1931

I suggest changing that as follows:
```fortran
if (croplive(p) .and. idop(p) <= jday .and. sowing_count(p) == 0) then
! Special handling for incorrect Dec. 31 plantings
if (is_beg_curr_year() .and. idop(p) == 1) then
crop_inst%sdates_thisyr_patch(p,1) = avg_dayspyr
else
sowing_count(p) = 1
crop_inst%sdates_thisyr_patch(p,1) = real(idop(p), r8)
end if
end if
```

These criteria for special handling are intentionally strict. We only _know_ that a planting was incorrectly on Dec. 31 if its `idop` says it was planted Jan. 1 (i.e., day 1) but right now it's the first timestep of the year and we haven't yet reached the "should we plant today" checks.

Ideally I would set sdate to the number of days in the previous year, but I haven't looked into how to do that yet, so for now I just put `avg_dayspyr`. (There is no difference for calendars that don't include leap years.)

### Important details of your setup / configuration so we can reproduce the bug

I'm seeing this behavior in a startup run with a 2-degree `IHIST` compset starting 1850-01-01.