Check if the number of impactors in the subpixel diffusion step is bi…

…gger than the I8B maximum size. If so, skip, though it may be beneficial to let the user know they may need to truncate their production population.

src/crater/crater_subpixel_diffusion.f90

@@ -94,6 +94,7 @@ subroutine crater_subpixel_diffusion(user,surf,nflux,domain,finterval,kdiffin)
          end if
 
          lambda = dN * domain%parea
+         if (lambda > 1.0_DP * huge(N)) cycle ! Too many impactors. 
 
          ! Don't parallelize the random
          do j = 1,user%gridsize