vici: Return default value for get_int() if message value is empty string

This is the behavior of some strtol() implementations, and it makes sense,
so force it.

src/libcharon/plugins/vici/suites/test_message.c

@@ -347,7 +347,7 @@ START_TEST(test_get_int)
 	ck_assert_int_eq(m->get_int(m, 2, "section1.key2"), 0x12);
 	ck_assert_int_eq(m->get_int(m, 2, "section1.section2.key3"), -1);
 	ck_assert_int_eq(m->get_int(m, 2, "section1.key4"), 2);
-	ck_assert_int_eq(m->get_int(m, 2, "key5"), 0);
+	ck_assert_int_eq(m->get_int(m, 2, "key5"), 2);
 	ck_assert_int_eq(m->get_int(m, 2, "nonexistent"), 2);
 	ck_assert_int_eq(m->get_int(m, 2, "n.o.n.e.x.i.s.t.e.n.t"), 2);
 

src/libcharon/plugins/vici/vici_message.c

@@ -355,6 +355,10 @@ METHOD(vici_message_t, vget_int, int,
 	found = find_value(this, &value, fmt, args);
 	if (found)
 	{
+		if (value.len == 0)
+		{
+			return def;
+		}
 		if (chunk_printable(value, NULL, 0))
 		{
 			snprintf(buf, sizeof(buf), "%.*s", (int)value.len, value.ptr);