Reject reserved values and indefinite lengths

RFC 8949 defines additional information values 28, 29, 30 and 31 as
either reserved or indicating indefinite length values. Reject all of
these.

Test: cppbor_host_test_external
Change-Id: Ic9ae7630c8f75d060e4199d375c1f696699a4f66
diff --git a/src/cppbor_parse.cpp b/src/cppbor_parse.cpp
index 5cf76b2..fcf0dac 100644
--- a/src/cppbor_parse.cpp
+++ b/src/cppbor_parse.cpp
@@ -202,8 +202,13 @@
 
     bool success = true;
     uint64_t addlData;
-    if (tagInt < ONE_BYTE_LENGTH || tagInt > EIGHT_BYTE_LENGTH) {
+    if (tagInt < ONE_BYTE_LENGTH) {
         addlData = tagInt;
+    } else if (tagInt > EIGHT_BYTE_LENGTH) {
+        parseClient->error(
+                begin,
+                "Reserved additional information value or unsupported indefinite length item.");
+        return {begin, nullptr};
     } else {
         switch (tagInt) {
             case ONE_BYTE_LENGTH: