warnings after uncompressed_length 
 
UNCOMPRESSED_LENGTH() did not validate its argument. In 
particular, if the argument length was less than 4 bytes, 
an uninitialized memory value was returned as a result. 
 
Since the result of COMPRESS() is either an empty string or 
a 4-byte length prefix followed by compressed data, the bug was 
fixed by ensuring that the argument of UNCOMPRESSED_LENGTH() is 
either an empty string or contains at least 5 bytes (as done in 
UNCOMPRESS()). This is the best we can do to validate input 
without decompressing. 

mysql-test/r/func_compress.result:
  Added a test case for bug #44796.
mysql-test/t/func_compress.test:
  Added a test case for bug #44796.
sql/item_strfunc.cc:
  Make sure that the argument of UNCOMPRESSED_LENGTH() contains 
  at least 5 bytes (as done in UNCOMPRESS()).