Limit fire btran2 to be <= 1

For the older version calculated in CNFireBaseMod, btran2 could
sometimes be roundoff-level greater than 1. Due to a conditional in
CNFireArea, these slightly-greater-than-1 values were being ignored when
computing btran_col, rather than averaging in a 1 value.

I haven't investigated the behavior in the new version in
CNFireLi2021Mod, but it seems like this could have the same issue. It's
also possible, though, that we'd exceed 1 by more than roundoff in that
version under some conditions, if h2osoi_vol > watsat in some
layers. The endrun call will tell us if that's happening. Note that I
plan to remove the endrun call after initial testing, because it seems
like the correct thing to do here is to limit the btran2 value to be no
more than 1 even if it exceeds 1 by more than roundoff.

src/biogeochem/CNFireBaseMod.F90

@@ -255,6 +255,19 @@ subroutine CNFire_calc_fire_root_wetness( this, bounds, num_exposedvegp, filter_
                     (smpso(patch%itype(p)) - smpsc(patch%itype(p))), 1._r8))
          end do
       end do
+
+      do f = 1, num_exposedvegp
+         p = filter_exposedvegp(f)
+         if (btran2(p) > 1._r8) then
+            ! FIXME(wjs, 2020-10-02) remove this endrun conditional
+            if (btran2(p) > (1._r8 + 1.e-12_r8)) then
+               write(iulog,*) 'btran2 exceeds 1 by too much: ', p, btran2(p)
+               call endrun('btran2 exceeds 1 by too much')
+            end if
+            btran2(p) = 1._r8
+         end if
+      end do
+
     end associate 
 
   end subroutine CNFire_calc_fire_root_wetness

src/biogeochem/CNFireLi2021Mod.F90

@@ -720,6 +720,19 @@ subroutine CNFire_calc_fire_root_wetness( this, bounds, num_exposedvegp, filter_
             btran2(p)   = btran2(p) + rootfr(p,j)*s_node
          end do
       end do
+
+      do f = 1, num_exposedvegp
+         p = filter_exposedvegp(f)
+         if (btran2(p) > 1._r8) then
+            ! FIXME(wjs, 2020-10-02) remove this endrun conditional
+            if (btran2(p) > (1._r8 + 1.e-12_r8)) then
+               write(iulog,*) 'btran2 exceeds 1 by too much: ', p, btran2(p)
+               call endrun('btran2 exceeds 1 by too much')
+            end if
+            btran2(p) = 1._r8
+         end if
+      end do
+
     end associate 
 
  end subroutine CNFire_calc_fire_root_wetness