Re-initialize fields within KPP

Five fields associated with KPP were previously initialized during
allocation (using `source=0.`).  It was found that the allocations were
unnecessary, and the fields were redefined as local variables within
functions, without the initialization to zero.

Although the uninitialized points were masked and unused in the rest of
the model, they were still able to change the checksums and were being
reported as regressions.  This patch restores the original checksums by
re-implementing the zero initialization.

Thanks to Bob Hallberg (@Hallberg-NOAA) for diagnosing this issue.

src/parameterizations/vertical/MOM_diabatic_driver.F90

@@ -676,6 +676,14 @@ subroutine diabatic_ALE_legacy(u, v, h, tv, BLD, fluxes, visc, ADp, CDp, dt, Tim
     call cpu_clock_begin(id_clock_kpp)
     ! total vertical viscosity in the interior is represented via visc%Kv_shear
 
+    ! NOTE: The following do not require initialization, but their checksums do
+    !   require initialization, and past versions were initialized to zero.
+    KPP_NLTheat(:,:,:) = 0.
+    KPP_NLTscalar(:,:,:) = 0.
+    KPP_buoy_flux(:,:,:) = 0.
+    KPP_temp_flux(:,:) = 0.
+    KPP_salt_flux(:,:) = 0.
+
     ! KPP needs the surface buoyancy flux but does not update state variables.
     ! We could make this call higher up to avoid a repeat unpacking of the surface fluxes.
     ! Sets: KPP_buoy_flux, KPP_temp_flux, KPP_salt_flux
@@ -1288,6 +1296,14 @@ subroutine diabatic_ALE(u, v, h, tv, BLD, fluxes, visc, ADp, CDp, dt, Time_end,
       visc%Kv_shear(i,j,k) = visc%Kv_shear(i,j,k) + visc%Kv_slow(i,j,k)
     enddo ; enddo ; enddo
 
+    ! NOTE: The following do not require initialization, but their checksums do
+    !   require initialization, and past versions were initialized to zero.
+    KPP_NLTheat(:,:,:) = 0.
+    KPP_NLTscalar(:,:,:) = 0.
+    KPP_buoy_flux(:,:,:) = 0.
+    KPP_temp_flux(:,:) = 0.
+    KPP_salt_flux(:,:) = 0.
+
     ! KPP needs the surface buoyancy flux but does not update state variables.
     ! We could make this call higher up to avoid a repeat unpacking of the surface fluxes.
     ! Sets: KPP_buoy_flux, KPP_temp_flux, KPP_salt_flux
@@ -1885,6 +1901,15 @@ subroutine layered_diabatic(u, v, h, tv, BLD, fluxes, visc, ADp, CDp, dt, Time_e
 
   if (CS%useKPP) then
     call cpu_clock_begin(id_clock_kpp)
+
+    ! NOTE: The following do not require initialization, but their checksums do
+    !   require initialization, and past versions were initialized to zero.
+    KPP_NLTheat(:,:,:) = 0.
+    KPP_NLTscalar(:,:,:) = 0.
+    KPP_buoy_flux(:,:,:) = 0.
+    KPP_temp_flux(:,:) = 0.
+    KPP_salt_flux(:,:) = 0.
+
     ! KPP needs the surface buoyancy flux but does not update state variables.
     ! We could make this call higher up to avoid a repeat unpacking of the surface fluxes.
     ! Sets: KPP_buoy_flux, KPP_temp_flux, KPP_salt_flux