Fix Map decoding in presence of optional long byte-length marker

[fieldstrength]

I encountered a problem where messages that have an Avro Map produced by certain other Avro libraries were not decoding, and I noticed that we are not decoding maps properly in the presence of this optional byte-length indicator.

If a block’s count is negative, its absolute value is used, and the count is followed immediately by a long block size indicating the number of bytes in the block. This block size permits fast skipping through data, e.g., when projecting a record to a subset of its fields.

• https://avro.apache.org/docs/1.11.1/specification/#complex-types-1

[HuwCampbell]

Thanks!

That looks ok, but, the documentation also states this is so for arrays as well as maps.

It you could please:

• Include the fixup for arrays as well as maps
• Add the prose from the documentation to the code where it makes sense

That would be great and I'll merge

[HuwCampbell]

Ta