Only try to access irrig_method for CFTs

Without this, in runs with create_crop_landunit false, we run into
problems trying to access irrig_method for the irrigated generic crop,
which falls outside the bounds of clm_varsur's irrig_method array:

   at /gpfs/fs1/work/sacks/ctsm_code/current_branch1/src/biogeophys/IrrigationMod.F90:715

   Fortran runtime error: Index '16' of dimension 2 of array 'irrig_method' below lower bound of 17

I'm not sure we want this check long-term, but we need it at least until
the code for irrig_method is generalized to work with
create_crop_landunit false.

src/biogeophys/IrrigationMod.F90

@@ -50,7 +50,7 @@ module IrrigationMod
   use pftconMod        , only : pftcon
   use clm_varctl       , only : iulog
   use clm_varcon       , only : isecspday, denh2o, spval, ispval, namec, nameg
-  use clm_varpar       , only : nlevsoi, nlevgrnd
+  use clm_varpar       , only : nlevsoi, nlevgrnd, cft_lb, cft_ub
   use clm_time_manager , only : get_step_size
   use SoilWaterRetentionCurveMod, only : soil_water_retention_curve_type
   use WaterFluxBulkType      , only : waterfluxbulk_type
@@ -710,8 +710,8 @@ subroutine SetIrrigMethod(this, bounds)
 
     do p = bounds%begp,bounds%endp
        g = patch%gridcell(p)
-       if (pftcon%irrigated(patch%itype(p)) == 1._r8) then
-          m = patch%itype(p)
+       m = patch%itype(p)
+       if (m >= cft_lb .and. m <= cft_ub .and. pftcon%irrigated(m) == 1._r8) then
           this%irrig_method_patch(p) = irrig_method(g,m)
           ! ensure irrig_method is valid; if not set, use drip irrigation
           if(irrig_method(g,m) == irrig_method_unset) then