du-high: add extra validation checks for coreset0 config to avoid arm compilation issue

Author: frankist

lib/du/du_cell_config_validation.cpp

@@ -525,10 +525,12 @@ static check_outcome check_tdd_ul_dl_config(const du_cell_config& cell_cfg)
   // See TS 38.214, Table 5.1.2.1-1: Valid S and L combinations.
   static const unsigned pdsch_mapping_typeA_min_L_value = 3;
 
-  const pdcch_config_common&            common_pdcch_cfg = cell_cfg.dl_cfg_common.init_dl_bwp.pdcch_common;
-  const pdcch_config&                   ded_pdcch_cfg    = cell_cfg.ue_ded_serv_cell_cfg.init_dl_bwp.pdcch_cfg.value();
-  const optional<coreset_configuration> coreset0         = common_pdcch_cfg.coreset0;
-  const optional<coreset_configuration> common_coreset   = common_pdcch_cfg.common_coreset;
+  const pdcch_config_common&             common_pdcch_cfg = cell_cfg.dl_cfg_common.init_dl_bwp.pdcch_common;
+  const pdcch_config&                    ded_pdcch_cfg    = cell_cfg.ue_ded_serv_cell_cfg.init_dl_bwp.pdcch_cfg.value();
+  const optional<coreset_configuration>& coreset0         = common_pdcch_cfg.coreset0;
+  const optional<coreset_configuration>& common_coreset   = common_pdcch_cfg.common_coreset;
+  CHECK_TRUE(coreset0.has_value(), "CORESET#0 not configured");
+
   const pdcch_type0_css_occasion_pattern1_description ss0_occasion = pdcch_type0_css_occasions_get_pattern1(
       pdcch_type0_css_occasion_pattern1_configuration{.is_fr2        = false,
                                                       .ss_zero_index = static_cast<uint8_t>(cell_cfg.searchspace0_idx),