Description:
------------
I have opened a .gz file using gzopen for reading.
I can pass SEEK_END with offset of 0 (which would seek to the end of the file) using either fseek or gzseek as a whence. This returns -1 (a failure), but a subsequent gztell/ftell returns false, but I can still read the stream from the position it was last in. 

The issue is
1. is a whence of SEEK_END supported for a zlib stream ? If it is then SEEK_END is very broken as it doesn't move it to the end of the stream.

2. if not supported, I should get a warning saying invalid parameter. Also a subsequent call to gztell/ftell returns false.a further read and gztell/ftell returns an incorrect value 

I couldn't find any information to say it was not a valid value so assumed that it was valid.

Reproduce code:
---------------
<?php
//004.txt.gz taken from zlib test directory
//first 20 bytes are: "When you're taught t"
$f = dirname(__FILE__)."/004.txt.gz";
$h = gzopen($f, 'r'); 
//read the first 10
var_dump(gzread($h, 10));
echo "move to the end\n";
echo "gzseek=";
var_dump(gzseek( $h, 0, SEEK_END ) );
echo "tell=";
var_dump(gztell($h));
echo "eof=";
var_dump(gzeof($h));
//read the next 10
var_dump(gzread($h, 10));
echo "tell=";
var_dump(gztell($h));
?>

Expected result:
----------------
If SEEK_END is not valid:
string(10) "When you'r"
move to the end
gzseek=
Warning: gzseek() SEEK_END not supported
tell=int(10)
eof=bool(false)
string(10) "e taught t"
tell=int(20)

if SEEK_END is valid:
string(10) "When you'r"
move to the end
gzseek=int(0)
tell=int(176)
eof=bool(true)
string(0) ""
tell=int(176)

Actual result:
--------------
string(10) "When you'r"
move to the end
gzseek=int(-1)
tell=bool(false)
eof=bool(false)
string(10) "e taught t"
tell=int(9)