SAL: Explicitly allocate sht variable in SAL_CS

For reasons not entirely clear, deallocation of the RK2 control
structure caused a segmentation fault when compiled by Nvidia.  A deeper
investigation suggested that the compiler was attempting to deallocate a
nullified pointer during automatic cleanup of RK2->SAL->sht.  Apparently
deallocation of a NULL pointer is an error (even though free() is not
supposed to care).

By redefining `sht` as an allocatable component rather than a local
component of the SAL_CS instance, it seemed to satisfy the compiler that
nothing was needed and the error went away.

There are still some lingering questions behind the cause of the
segfault, but for now I am going to put this under "compiler bug".

This patch also initializes some of the logical flags in the SAL_CS
type.  This is possibly unnecessary, but it is consistent with the
general rules of safety followed in other MOM6 derived types.

src/parameterizations/lateral/MOM_self_attr_load.F90

@@ -20,14 +20,17 @@ module MOM_self_attr_load
 
 !> The control structure for the MOM_self_attr_load module
 type, public :: SAL_CS ; private
-  logical :: use_sal_scalar     !< If true, use the scalar approximation to calculate SAL.
-  logical :: use_sal_sht        !< If true, use online spherical harmonics to calculate SAL
-  logical :: use_tidal_sal_prev !< If true, read the tidal SAL from the previous iteration of
-                                !! the tides to facilitate convergence.
+  logical :: use_sal_scalar = .false.
+    !< If true, use the scalar approximation to calculate SAL.
+  logical :: use_sal_sht = .false.
+    !< If true, use online spherical harmonics to calculate SAL
+  logical :: use_tidal_sal_prev = .false.
+    !< If true, read the tidal SAL from the previous iteration of the tides to
+    !! facilitate convergence.
   real    :: sal_scalar_value   !< The constant of proportionality between sea surface height
                                 !! (really it should be bottom pressure) anomalies and bottom
                                 !! geopotential anomalies [nondim].
-  type(sht_CS) :: sht           !< Spherical harmonic transforms (SHT) control structure
+  type(sht_CS), allocatable :: sht  !< Spherical harmonic transforms (SHT) control structure
   integer :: sal_sht_Nd         !< Maximum degree for SHT [nodim]
   real, allocatable :: Love_Scaling(:) !< Love number for each SHT mode [nodim]
   real, allocatable :: Snm_Re(:), &    !< Real SHT coefficient for SHT SAL [Z ~> m]
@@ -218,6 +221,8 @@ subroutine SAL_init(G, US, param_file, CS)
 
     allocate(CS%Love_Scaling(lmax)); CS%Love_Scaling(:) = 0.0
     call calc_love_scaling(CS%sal_sht_Nd, rhoW, rhoE, CS%Love_Scaling)
+
+    allocate(CS%sht)
     call spherical_harmonics_init(G, param_file, CS%sht)
   endif
 
@@ -234,6 +239,7 @@ subroutine SAL_end(CS)
     if (allocated(CS%Snm_Re)) deallocate(CS%Snm_Re)
     if (allocated(CS%Snm_Im)) deallocate(CS%Snm_Im)
     call spherical_harmonics_end(CS%sht)
+    deallocate(CS%sht)
   endif
 end subroutine SAL_end