kv_engine accepts doc bigger than 20mb when compressed

Hi,

when working on compression with the java SDK i found that kv_engine seems to accept docs larger than 20mb but rejects it properly without compression.

I could reproduce it with lcb/cbc too so its easy to repro.

1) I have a file called OUT which is exactly 21k bytes long containing only the char lowercase L

$ wc -c < OUT

 21000000

When storing it via cbc without compression (2.8.5) it gets rejected:

$ cbc create -u Administrator -P password mydoc < OUT

mydoc                The object requested is too big to store in the server (0x4)

Doing the same thing with compression enabled (-y -y) accepts the doc:

$ cbc create -u Administrator -P password mydoc -y -y < OUT

mydoc               Stored. CAS=0x1524f8b9c12b0000

You can see it now int he UI as "binary doc" and its longer than allowed.