Description:
------------
user aggregate function on empty select result
Apache crach


Reproduce code:
---------------
function actstep(&$context,$tau,$val) {
   if ($conext[0]<$tau) { $conext[0]=$tau; $context[1]=$val; }
   }
function actfin(&$context) {
   return $context[1];
   }
$f = 'tmp.sqlt';
unlink($f);
$h = sqlite_open($f);
sqlite_exec($h,"CREATE TABLE lnk(obj,atr,tau,val)");
sqlite_exec($h,"INSERT INTO lnk VALUES(1,1,2,5)");
sqlite_exec($h,"INSERT INTO lnk VALUES(1,1,5,10)");
sqlite_create_aggregate($h,'actual','actstep','actfin');

// This work:
$r1 = sqlite_array_query($h,"SELECT actual(tau,val) FROM lnk WHERE obj=1 AND atr=1 AND tau<=10",SQLITE_NUM);
// When empty result set Apache crach: 
$r2 = sqlite_array_query($h,"SELECT actual(tau,val) FROM lnk WHERE obj=2 AND atr=1 AND tau<=10",SQLITE_NUM);
var_dump($r1);
var_dump($r2);


Expected result:
----------------
array(1) { [0]=> array(1) { [0]=> string(2) "10" } }
null 

Actual result:
--------------
Crach