OSS-Fuzz failed throw issue in CBOR parser (22000)

[danielaparker]

Issue 1:

Bad input resulted in a JSONCONS_ASSERT failure when checking that an array containing a decimal fraction had the required two elements. The assert has been replaced by error code cbor_errc::invalid_decimal_fraction.

Issue 2:

prettify_string with decimal fractions failed with exponents >= 1000.

These issues have been verified as fixed in v0.151.0 by OSS-Fuzz.