Uncaught exception in CBORParser._findDecodedFromSymbols()

[cowtowncoder]

(note: original report at https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=35750)

Looks like non-canonical length definition (using long form for length of 0) will result in an exception; needs to be checked.

A related question would be whether there should be "strict" decoding mode as this is violation of canonical form.
But first thing first, handle this case gracefully.