[v2.15.0] `recipe_ipccwg1ar6ch3_atmosphere.yml` NCL diagnostic script fails

[flicj191]

DiagnosticError: An error occurred during execution of NCL script ipcc_ar6/precip_anom.ncl

INFO    Process dataset: MultiModelMean
INFO    Reading in file = /scratch/tm70/fc6164/esmvaltool_output/recipe_ipccwg1ar6ch3_atmosphere_20260713_005941/preproc/fig_3_15_precip_anom/pr_hist-nat_global/MultiModelMean_hist-nat_Amon_pr_1950-2014.nc
fatal:Subscript out of range, error in subscript #0

fatal:An error occurred reading model_arr_em

fatal:["Execute.c":8637]:Execute: Error occurred at or near line 428 in file /home/189/fc6164/esmValTool/repos/ESMVal/ESMValTool/esmvaltool/diag_scripts/ipcc_ar6/precip_anom.ncl