- Add a check that length of field to uncompress is longer than 4 bytes.
   This can be dones as the length of uncompressed data is written as 
   first four bytes of field and thus it can't be valid compressed data.


mysql-test/r/func_compress.result:
  Update test results
sql/item_strfunc.cc:
  Is size of field is less than or equal to 4 bytes, indicate data is uncompressable/corrupt.