Added an optimisation which reduced the number of queries executed in the
View Bugs page when "All Projects" is selected from 314 to 220. This is that
the project specific user access level is not retrieved from the database
because in this case the project cookie is set to 0, and there is no project
with code 0. In this case, the general access level is used.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@1167 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9