Description:
------------
I'm using libgearman 0.11 with PECL PHP extension gearman 
0.6.0 on CentOS 5.4 using Apache 2.2 and PHP 5.3.

While running a Gearman Worker I got this error:
php: client.c:773: gearman_client_run_tasks: Assertion 
`client->task != ((void *)0)`failed.

Context; I made this PHP script:
http://pastie.org/private/jzm9ox4kogpllz9onl7ma

When I start one worker, everything goes smooth. When I 
start an additional second worker, no problem. When I start 
the third worker, the first worker crashes with the error 
above. At the moment the third worker starts, it registers 
to the first worker (addNeighbour). This 'addNeighbour' will 
call the 'updateNeighbour' function on the first Worker 
itself. In the loop, the IF-statement will return false for 
the first time, so the else-part is executed. When it comes 
to #110 the crash occurs.

Little strange to me is that after the first worker crashed, 
I can start as many additional workers as I like... they 
won't crash.

This bug keeps me from using Gearman in PHP at the moment. 
Thanks in advance!


This bug is replicated on Gearman itself: 
https://bugs.launchpad.net/gearmand/+bug/518512

Reproduce code:
---------------
http://pastie.org/private/jzm9ox4kogpllz9onl7ma

Expected result:
----------------
Nothing, just running the jobs, adding the neighbour and 
update others.

Actual result:
--------------
php: client.c:773: gearman_client_run_tasks: Assertion 
`client->task != ((void *)0)`failed.