Include original error for invalid error error message

So that it is still possible to see the error message which was being
reported.

Author: thomasspriggs

src/solvers/smt2_incremental/smt_response_validation.cpp

@@ -175,7 +175,8 @@ valid_smt_error_response(const irept &parse_tree)
   if(parse_tree.get_sub().size() > 2)
   {
     return {response_or_errort<smt_responset>{
-      "Error response has multiple error messages."}};
+      "Error response has multiple error messages - \"" +
+      print_parse_tree(parse_tree) + "\"."}};
   }
   return validation_propagating<smt_error_responset, smt_responset>(
     validate_string_literal(parse_tree.get_sub()[1]));

unit/solvers/smt2_incremental/smt_response_validation.cpp

@@ -90,7 +90,10 @@ TEST_CASE("Validation of SMT error response", "[core][smt2_incremental]")
        *smt2irep("(error \"Test error message1.\" \"Test error message2.\")")
           .parsed_output)
        .get_if_error() ==
-    std::vector<std::string>{"Error response has multiple error messages."});
+    std::vector<std::string>{"Error response has multiple error messages - \"\n"
+                             "0: error\n"
+                             "1: Test error message1.\n"
+                             "2: Test error message2.\"."});
 }
 
 TEST_CASE("smt get-value response validation", "[core][smt2_incremental]")