Fix crash with internal assertion on short array initializer (partial #5511)

src/V3EmitCConstInit.h

@@ -82,7 +82,9 @@ protected:
             for (uint64_t n = 0; n < size; ++n) {
                 m_unpackedWord = n;
                 if (n) puts((n % tabMod) ? ", " : ",\n");
-                iterateConst(nodep->getIndexDefaultedValuep(n));
+                AstNode* const itemp = nodep->getIndexDefaultedValuep(n);
+                UASSERT_OBJ(itemp, nodep, "Missing array init element");
+                iterateConst(itemp);
             }
             puts("\n");
             puts("}");

test_regress/t/t_unpacked_concat_bad3.out

@@ -0,0 +1,4 @@
+%Error: Internal Error: t/t_unpacked_concat_bad3.v:9:41: ../V3EmitCConstInit.h:#: Missing array init element
+    9 |    localparam logic [7:0] TOO_FEW [5] = '{0, 1, 2**8-1};   
+      |                                         ^~
+                        ... See the manual at https://verilator.org/verilator_doc.html for more assistance.

test_regress/t/t_unpacked_concat_bad3.py

@@ -0,0 +1,17 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2024 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('vlt')
+
+# Not lint, crashes in V3EmitCConstInit.h
+test.compile(fails=True, expect_filename=test.golden_filename)
+
+test.passes()

test_regress/t/t_unpacked_concat_bad3.v

@@ -0,0 +1,15 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2019 by Driss Hafdi.
+// SPDX-License-Identifier: CC0-1.0
+
+module t (/*AUTOARG*/);
+
+   localparam logic [7:0] TOO_FEW [5] = '{0, 1, 2**8-1};  // Bad
+
+   initial begin
+      $display("%p", TOO_FEW);
+      $stop;
+   end
+endmodule