Steps to produce the issue:
 1. start up roundup demo.py
 2. have at least two issue in the system (create two dummy ones if needed)
 3. browse to:
      http://localhost:8917/demo/issue?@startwith=1&@pagesize=0
 4. look at the "previous" link and notice it is something like:
      http://localhost:8917/demo/issue?@startwith=1&@pagesize=7
    (ie. the '@pagesize=0' is not propagated, but instead changed to
'@pagesize=7')

This is and issue if you don't want '@pagesize=0' change to
'@pagesize=7' (ie: see issue2550678)

Apply the patch and '@pagesize=0' should be propagated correctly.