Fix crash during dealing with empty optinal fields of ioc cell

libasn1compiler/asn1c_C.c

@@ -1070,6 +1070,8 @@ asn1c_lang_C_OpenType(arg_t *arg, asn1c_ioc_table_and_objset_t *opt_ioc,
         struct asn1p_ioc_cell_s *cell =
             &opt_ioc->ioct->row[row]->column[column_index];
 
+        if(!cell->value) continue;
+
         asn1p_expr_t *m = asn1p_expr_clone(cell->value, 0);
         asn1p_expr_add(open_type_choice, m);
     }

libasn1compiler/asn1c_ioc.c

@@ -213,7 +213,9 @@ static int
 emit_ioc_cell(arg_t *arg, struct asn1p_ioc_cell_s *cell) {
     OUT("{ \"%s\", ", cell->field->Identifier);
 
-    if(cell->value->meta_type == AMT_VALUE) {
+    if(!cell->value) {
+        /* Ignore */
+    } else if(cell->value->meta_type == AMT_VALUE) {
         GEN_INCLUDE(asn1c_type_name(arg, cell->value, TNF_INCLUDE));
         OUT("aioc__value, ");
         OUT("&asn_DEF_%s, ", asn1c_type_name(arg, cell->value, TNF_SAFE));