Remove C null characters from strings read by PIO

The PIO2 library fills in unused characters of a string variable with
C null characters, and replaces C null characters with spaces when reading
strings. However, the PIO1 library does not perform these conversions.
Consequently, if a file written by the PIO2 library is read by the PIO1 library,
C null characters may be present in the resulting Fortran string.

Under the assumption that C null characters will generally not be expected
or handled in MPAS (e.g., in timestamp strings), this commit makes calls to
MPAS_sanitize_string to convert any C null characters in strings read by PIO
into spaces.

Author: mgduda

src/framework/mpas_io.F

@@ -2187,6 +2187,8 @@ end subroutine MPAS_io_get_var_real5d
 
    subroutine MPAS_io_get_var_char0d(handle, fieldname, val, ierr)
 
+      use mpas_c_interfacing, only : MPAS_sanitize_string
+
       implicit none
 
       type (MPAS_IO_Handle_type), intent(inout) :: handle
@@ -2198,23 +2200,31 @@ subroutine MPAS_io_get_var_char0d(handle, fieldname, val, ierr)
       if (present(ierr)) ierr = MPAS_IO_NOERR
 
       call MPAS_io_get_var_generic(handle, fieldname, charVal=val, ierr=ierr)
+      call MPAS_sanitize_string(val)
 
    end subroutine MPAS_io_get_var_char0d
 
 
    subroutine MPAS_io_get_var_char1d(handle, fieldname, val, ierr)
 
+      use mpas_c_interfacing, only : MPAS_sanitize_string
+
       implicit none
 
       type (MPAS_IO_Handle_type), intent(inout) :: handle
       character (len=*), intent(in) :: fieldname
       character (len=*), dimension(:), intent(out) :: val
       integer, intent(out), optional :: ierr
 
+      integer :: i
+
 !     call mpas_log_write('Called MPAS_io_get_var_char1d()')
       if (present(ierr)) ierr = MPAS_IO_NOERR
 
       call MPAS_io_get_var_generic(handle, fieldname, charArray1d=val, ierr=ierr)
+      do i=1,size(val)
+         call MPAS_sanitize_string(val(i))
+      end do
 
    end subroutine MPAS_io_get_var_char1d