[ticket/16141] plupload chunk_size when 'unlimited' is involved.

Change get_chunk_size() calculation to correctly calculate limits without
letting a zero "unlimited" value always win.  Also ensure get_chunk_size()
can only return zero if all of the limits were in fact set to unlimited.

PHPBB3-16141

phpBB/phpbb/plupload/plupload.php

@@ -314,7 +314,7 @@ class plupload
 		{
 			$max = min($limit_post, ($max ? $max : $limit_post));
 		}
-		
+
 		// $config['max_filesize'] is not a limiter to chunk size.
 
 		return floor($max / 2);